diff --git a/.github/workflows/Lint.yml b/.github/workflows/Lint.yml
new file mode 100644
index 0000000..4567bfc
--- /dev/null
+++ b/.github/workflows/Lint.yml
@@ -0,0 +1,58 @@
+name: Lint
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    types: [opened, synchronize]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php: ['5.3', '5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          tools: composer:v2
+
+      - name: Lint
+        run: |
+          error=0
+          for file in $(find Trustly -type f -name "*.php"); do
+            php -l -n $file | grep -v "No syntax errors detected" && error=1
+          done
+          if [ $error -eq 1 ]; then
+            echo "Syntax errors were found."
+            exit 1
+          else
+            echo "No syntax errors were detected."
+          fi
+
+      - name: Cache dependencies
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/composer/files
+          key: ${{ matrix.php }}-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ matrix.php }}-
+
+      - name: Check dependencies
+        run: composer install
+
+      - name: PHPStan
+        if: ${{ startsWith(matrix.php, '7.') || startsWith(matrix.php, '8.') }}
+        run: |
+          composer require --dev phpstan/phpstan
+          vendor/bin/phpstan analyze Trustly --no-progress --level 7
diff --git a/.gitignore b/.gitignore
index e52ccc1..e005a0c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
 example/var/
+/vendor
+/composer.lock
diff --git a/Trustly/Api/api.php b/Trustly/Api/api.php
index c9fee7d..5c5cfc4 100644
--- a/Trustly/Api/api.php
+++ b/Trustly/Api/api.php
@@ -44,13 +44,13 @@ abstract class Trustly_Api {
 	 *
 	 * @var string FQHN
 	 */
-	protected $api_host = NULL;
+	protected $api_host;
 	/**
 	 * API port used for communication.
 	 *
 	 * @var integer Normally either 443 (https) or 80 (http)
 	 */
-	protected $api_port = NULL;
+	protected $api_port;
 	/**
 	 * Inidicator wether the API host is communicating using https
 	 *
@@ -63,10 +63,13 @@ abstract class Trustly_Api {
 	 *
 	 * @see Trustly_Api::getLastRequest()
 	 *
-	 * @var array Last API call in data form.
+	 * @var ?Trustly_Data_Request Last API call in data form.
 	 */
 	public $last_request = NULL;
 
+	/** @var mixed */
+	public $trustly_publickey = NULL;
+
 	/**
 	 * API Constructor
 	 *
@@ -89,9 +92,9 @@ abstract class Trustly_Api {
 	public function __construct($host='trustly.com', $port=443, $is_https=TRUE) {
 		$this->api_is_https = $is_https;
 
-		if($this->loadTrustlyPublicKey($host, $port, $is_https) === FALSE) {
+		if($this->loadTrustlyPublicKey($host, $port) === FALSE) {
 			$error = openssl_error_string();
-			throw new InvalidArgumentException("Cannot load Trustly public key file for host $host".(isset($error)?", error $error":''));
+			throw new InvalidArgumentException("Cannot load Trustly public key file for host $host".($error?", error $error":''));
 		}
 
 		/* Make sure the curl extension is loaded so we can open URL's */
@@ -139,9 +142,9 @@ public function loadTrustlyPublicKey($host, $port) {
 	 *
 	 * @link https://eu.developers.trustly.com/doc/reference/authentication
 	 *
-	 * @param array $data Input data to serialize
+	 * @param mixed $data Input data to serialize
 	 *
-	 * @return array The input data in a serialized form
+	 * @return string The input data in a serialized form
 	 */
 	public function serializeData($data) {
 		if(is_array($data)) {
@@ -167,13 +170,13 @@ public function serializeData($data) {
 	 *
 	 * @link https://eu.developers.trustly.com/doc/reference/authentication
 	 *
-	 * @param string $method Method in the API call
+	 * @param ?string $method Method in the API call
 	 *
-	 * @param string $uuid UUID in the API call
+	 * @param ?string $uuid UUID in the API call
 	 *
-	 * @param string $signature in the API call
+	 * @param ?string $signature in the API call
 	 *
-	 * @param array $data in the API call
+	 * @param mixed $data in the API call
 	 *
 	 * @return boolean Indicating wether or not the host key was used for
 	 *		signing this data.
@@ -204,7 +207,7 @@ protected function verifyTrustlySignedData($method, $uuid, $signature, $data) {
 	 * Trustly_Data_Response) has been signed with the correct key when
 	 * originating from the host
 	 *
-	 * @param Trustly_Data_Response $response Response from the API call.
+	 * @param Trustly_Data_JSONRPCSignedResponse $response Response from the API call.
 	 *
 	 * @return boolean Indicating if the data was indeed properly signed by the
 	 *		API we think we are talking to
@@ -223,7 +226,7 @@ public function verifyTrustlySignedResponse($response) {
 	 * Trustly_Data_JSONRPCNotificationRequest) has been signed with the
 	 * correct key originating from the host
 	 *
-	 * @param Trustly_Data_JSONRPCNotificationRequest incoming notification
+	 * @param Trustly_Data_JSONRPCNotificationRequest $notification incoming notification
 	 *
 	 * @return boolean Indicating if the data was indeed properly signed by the
 	 *		API we think we are talking to
@@ -243,15 +246,17 @@ public function verifyTrustlySignedNotification($notification) {
 	 * @throws InvalidArgumentException If the public key for the API host
 	 *		cannot be loaded.
 	 *
-	 * @param string $host API host used for communication. Fully qualified
+	 * @param ?string $host API host used for communication. Fully qualified
 	 *		hostname. When integrating with our public API this is typically
 	 *		either 'test.trustly.com' or 'trustly.com'. NULL means do not change.
 	 *
-	 * @param integer $port Port on API host used for communicaiton. Normally
+	 * @param ?integer $port Port on API host used for communicaiton. Normally
 	 *		443 for https, or 80 for http. NULL means do not change.
 	 *
-	 * @param bool $is_https Indicator wether the port on the API host expects
+	 * @param ?bool $is_https Indicator wether the port on the API host expects
 	 *		https. NULL means do not change.
+	 *
+	 * @return void
 	 */
 	public function setHost($host=NULL, $port=NULL, $is_https=NULL) {
 		if(!isset($host)) {
@@ -264,7 +269,7 @@ public function setHost($host=NULL, $port=NULL, $is_https=NULL) {
 
 		if($this->loadTrustlyPublicKey($host, $port) === FALSE) {
 			$error = openssl_error_string();
-			throw new InvalidArgumentException("Cannot load Trustly public key file for host $host".(isset($error)?", error $error":''));
+			throw new InvalidArgumentException("Cannot load Trustly public key file for host $host".($error?", error $error":''));
 		}
 
 		if(isset($is_https)) {
@@ -275,11 +280,11 @@ public function setHost($host=NULL, $port=NULL, $is_https=NULL) {
 	/**
 	 * Setup and return a curl handle for submitting data to the API peer.
 	 *
-	 * @param string $url The URL to communicate with
+	 * @param ?string $url The URL to communicate with
 	 *
-	 * @param string $postdata The (optional) data to post.
+	 * @param ?string $postdata The (optional) data to post.
 	 *
-	 * @return Array($body, $response_code)
+	 * @return array{string, int} Array($body, $response_code)
 	 */
 	public function post($url=NULL, $postdata=NULL) {
 		/* Do note that that if you are going to POST JSON you need to set the
@@ -295,13 +300,13 @@ public function post($url=NULL, $postdata=NULL) {
 		curl_setopt($curl, CURLOPT_PORT, $this->api_port);
 
 		if($this->api_is_https) {
-			if(@CURLOPT_PROTOCOLS != 'CURLOPT_PROTOCOLS') {
+			if(defined('CURLOPT_PROTOCOLS')) {
 				curl_setopt($curl, CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
 			}
 			curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, 2);
 			curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, TRUE);
 		} else {
-			if(@CURLOPT_PROTOCOLS != 'CURLOPT_PROTOCOLS') {
+			if(defined('CURLOPT_PROTOCOLS')) {
 				curl_setopt($curl, CURLOPT_PROTOCOLS, CURLPROTO_HTTP);
 			}
 		}
@@ -313,9 +318,9 @@ public function post($url=NULL, $postdata=NULL) {
 		curl_setopt($curl, CURLOPT_URL, $url);
 
 		$body = curl_exec($curl);
-		if($body === FALSE) {
+		if(!is_string($body)) {
 			$error = curl_error($curl);
-			if($error === NULL) {
+			if(!$error) {
 				$error = 'Failed to connect to the Trusly API';
 			}
 			throw new Trustly_ConnectionException($error);
@@ -378,7 +383,7 @@ public function post($url=NULL, $postdata=NULL) {
 	/**
 	 * Return a properly formed url to communicate with this API.
 	 *
-	 * @return URL pointing to the API peer.
+	 * @return string URL pointing to the API peer.
 	 */
 	public function baseURL() {
 		if($this->api_is_https) {
@@ -392,9 +397,9 @@ public function baseURL() {
 	/**
 	 * Return a URL to the API to the given request path.
 	 *
-	 * @param Trustly_Data_Request $request Data to send in the request
+	 * @param ?Trustly_Data_Request $request Data to send in the request
 	 *
-	 * @return URL to the API peer with the given query path.
+	 * @return string URL to the API peer with the given query path.
 	 */
 	public function url($request=NULL) {
 		return $this->baseURL() . $this->urlPath($request);
@@ -404,7 +409,7 @@ public function url($request=NULL) {
 	/**
 	 * Return the last request that we attempted to make via this API
 	 *
-	 * @return array Last request data structure.
+	 * @return ?Trustly_Data_Request Last request data structure.
 	 */
 	public function getLastRequest() {
 		return $this->last_request;
@@ -465,6 +470,7 @@ public function notificationResponse($request, $success=TRUE) {
 	 *
 	 * @param Trustly_Data_Request $request Outgoing data request.
 	 *
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function call($request) {
 		if($this->insertCredentials($request) !== TRUE) {
@@ -473,6 +479,9 @@ public function call($request) {
 		$this->last_request = $request;
 
 		$jsonstr = $request->json();
+		if($jsonstr === FALSE) {
+			throw new Trustly_DataException('Unable to json encode payload');
+		}
 
 		$url = $this->url($request);
 		list($body, $response_code) = $this->post($url, $jsonstr);
@@ -484,9 +493,9 @@ public function call($request) {
 	/**
 	 * Return a boolean value formatted for communicating with the API.
 	 *
-	 * @param boolean $value Boolean value to encode
+	 * @param ?boolean $value Boolean value to encode
 	 *
-	 * @return API encoded boolean value
+	 * @return ?string API encoded boolean value
 	 */
 	protected function apiBool($value) {
 		if(isset($value)) {
@@ -506,7 +515,7 @@ protected function apiBool($value) {
 	 *
 	 * See specific class implementing the call for more information.
 	 *
-	 * @param Trustly_Data_Request $request Data to send in the request
+	 * @param ?Trustly_Data_Request $request Data to send in the request
 	 *
 	 * @return string The URL path
 	 */
@@ -524,6 +533,8 @@ abstract protected function urlPath($request=NULL);
 	 * @param string $body The body recieved in response to the request
 	 *
 	 * @param integer $response_code the HTTP response code for the call
+	 *
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	abstract protected function handleResponse($request, $body, $response_code);
 
@@ -535,6 +546,8 @@ abstract protected function handleResponse($request, $body, $response_code);
 	 *
 	 * @param Trustly_Data_Request $request Request to be used in the outgoing
 	 *		call
+	 *
+	 * @return bool
 	 */
 	abstract protected function insertCredentials($request);
 
diff --git a/Trustly/Api/signed.php b/Trustly/Api/signed.php
index 69d0b5b..6e10810 100644
--- a/Trustly/Api/signed.php
+++ b/Trustly/Api/signed.php
@@ -37,10 +37,16 @@
 class Trustly_Api_Signed extends Trustly_Api {
 	/**
 	 * Loaded merchant private key resource
-	 * @var resource from openssl with the loaded privatekey
+	 * @var mixed from openssl with the loaded privatekey
 	 */
 	private $merchant_privatekey = NULL;
 
+	/** @var string */
+	public $api_username;
+
+	/** @var string */
+	public $api_password;
+
 	/**
 	 * Constructor.
 	 *
@@ -70,7 +76,7 @@ public function __construct($merchant_privatekey, $username, $password, $host='t
 		parent::__construct($host, $port, $is_https);
 
 		$this->api_username = $username;
-		$this->api_password  = $password;
+		$this->api_password = $password;
 		if($merchant_privatekey != NULL) {
 			if(strpos($merchant_privatekey, "\n") !== FALSE) {
 				if($this->useMerchantPrivateKey($merchant_privatekey) === FALSE) {
@@ -107,7 +113,9 @@ public function loadMerchantPrivateKey($filename) {
 	 *
 	 * @see https://eu.developers.trustly.com/doc/reference/authentication
 	 *
-	 * @param string $cert Loaded private RSA key as a string
+	 * @param string|false $cert Loaded private RSA key as a string
+	 *
+	 * @return bool
 	 */
 	public function useMerchantPrivateKey($cert) {
 		if($cert !== FALSE) {
@@ -124,7 +132,9 @@ public function useMerchantPrivateKey($cert) {
 	 * @throws Trustly_SignatureException if private key has not been loaded
 	 *		yet or if we for some other reason fail to sign the request.
 	 *
-	 * @param Trustly_Data_JSONRPCRequest $request Request to sign.
+	 * @param Trustly_Data_JSONRPCRequest|Trustly_Data_JSONRPCNotificationResponse $request Request to sign.
+	 *
+	 * @return string
 	 */
 	public function signMerchantRequest($request) {
 		if(!isset($this->merchant_privatekey)) {
@@ -166,9 +176,6 @@ protected function insertCredentials($request) {
 		$request->setData('Password', $this->api_password);
 
 		$signature = $this->signMerchantRequest($request);
-		if($signature === FALSE) {
-			return FALSE;
-		}
 		$request->setParam('Signature', $signature);
 
 		return TRUE;
@@ -194,7 +201,7 @@ protected function insertCredentials($request) {
 	 * @return Trustly_Data_JSONRPCSignedResponse
 	 */
 	protected function handleResponse($request, $body, $response_code) {
-		$response = new Trustly_Data_JSONRPCSignedResponse($body, $response_code);
+		$response = new Trustly_Data_JSONRPCSignedResponse($body);
 
 		if($this->verifyTrustlySignedResponse($response) !== TRUE) {
 			throw new Trustly_SignatureException('Incomming message signature is not valid', $response);
@@ -223,9 +230,6 @@ public function notificationResponse($request, $success=TRUE) {
 		$response = new Trustly_Data_JSONRPCNotificationResponse($request, $success);
 
 		$signature = $this->signMerchantRequest($response);
-		if($signature === FALSE) {
-			return FALSE;
-		}
 		$response->setSignature($signature);
 
 		return $response;
@@ -239,7 +243,7 @@ public function notificationResponse($request, $success=TRUE) {
 	 *
 	 * See specific class implementing the call for more information.
 	 *
-	 * @param Trustly_Data_JSONRPCRequest $request Data to send in the request
+	 * @param ?Trustly_Data_JSONRPCRequest $request Data to send in the request
 	 *
 	 * @return string The URL path
 	 */
@@ -251,6 +255,8 @@ protected function urlPath($request=NULL) {
 
 	/**
 	 * Quirks mode implementation of clearing all pending openssl error messages.
+	 *
+	 * @return void
 	 */
 	private function clearOpenSSLError() {
 		/* Not really my favourite part of this library implementation. As
@@ -303,7 +309,7 @@ protected function generateUUID() {
 	 *
 	 * @param Trustly_Data_JSONRPCRequest $request Outgoing request
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse Response from the API.
+	 * @return Trustly_Data_JSONRPCResponse Response from the API.
 	 */
 	public function call($request) {
 		$uuid = $request->getUUID();
@@ -437,7 +443,7 @@ public function call($request) {
 	 *		in the previously used account being preselected
 	 * @param bool $requestKYC Flag to pass whether we request KYC check or not (Pay N Play feature)
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function deposit($notificationurl, $enduserid, $messageid,
 		$locale=NULL, $amount=NULL, $currency=NULL, $country=NULL,
@@ -515,10 +521,10 @@ public function deposit($notificationurl, $enduserid, $messageid,
 	 * @param float $amount The amount to refund the customer with exactly two
 	 *		decimals. Only digits. Use dot (.) as decimal separator.
 	 *
-	 * @param string currency The currency of the amount to refund the
+	 * @param string $currency The currency of the amount to refund the
 	 *		customer.
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function refund($orderid, $amount, $currency) {
 
@@ -617,7 +623,7 @@ public function refund($orderid, $amount, $currency) {
 	 *
 	 * @param string $address The account holders address
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function withdraw($notificationurl, $enduserid, $messageid,
 		$locale=NULL, $currency=NULL, $country=NULL,
@@ -676,7 +682,7 @@ public function withdraw($notificationurl, $enduserid, $messageid,
 	 *
 	 * @param integer $orderid The OrderID of the withdrawal to approve.
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function approveWithdrawal($orderid) {
 
@@ -699,7 +705,7 @@ public function approveWithdrawal($orderid) {
 	 *
 	 * @param integer $orderid The OrderID of the withdrawal to deny.
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function denyWithdrawal($orderid) {
 
@@ -767,7 +773,7 @@ public function denyWithdrawal($orderid) {
 	 * @param boolean $requestdirectdebitmandate Initiate a direct debit
 	 *		mandate request for the selected account.
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function selectAccount($notificationurl, $enduserid, $messageid,
 		$locale=NULL, $country=NULL, $ip=NULL, $successurl=NULL, $urltarget=NULL,
@@ -860,7 +866,7 @@ public function selectAccount($notificationurl, $enduserid, $messageid,
 	 *
 	 * @param string $address The account holders address
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function registerAccount($enduserid, $clearinghouse, $banknumber,
 		$accountnumber, $firstname, $lastname, $mobilephone=NULL,
@@ -935,7 +941,7 @@ public function registerAccount($enduserid, $clearinghouse, $banknumber,
 	 *		system during development. Intead you can get you notifications on
 	 *		https://test.trustly.com/notifications.html
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function accountPayout($notificationurl, $accountid, $enduserid,
 		$messageid, $amount, $currency, $holdnotifications=NULL) {
@@ -980,76 +986,80 @@ public function accountPayout($notificationurl, $accountid, $enduserid,
 	 *
 	 * @param string $messageid Your unique ID for the deposit.
 	 *
-	 * @param string $locale The end-users localization preference in the
+	 * @param ?string $locale The end-users localization preference in the
 	 *		format [language[_territory]]. Language is the ISO 639-1 code and
 	 *		territory the ISO 3166-1-alpha-2 code.
 	 *
-	 * @param float $amount with exactly two decimals in the currency specified
+	 * @param ?float $amount with exactly two decimals in the currency specified
 	 *		by Currency. Do not use this attribute in combination with
 	 *		SuggestedMinAmount or SuggestedMaxAmount. Only digits. Use dot (.)
 	 *		as decimal separator.
 	 *
-	 * @param string $currency The currency of the end-user's account in the
+	 * @param ?string $currency The currency of the end-user's account in the
 	 *		merchant's system.
 	 *
-	 * @param string $country The ISO 3166-1-alpha-2 code of the end-user's
+	 * @param ?string $country The ISO 3166-1-alpha-2 code of the end-user's
 	 *		country. This will be used for preselecting the correct country for
 	 *		the end-user in the iframe.
 	 *
-	 * @param string $mobilephone The mobile phonenumber to the end-user in
+	 * @param ?string $mobilephone The mobile phonenumber to the end-user in
 	 *		international format. This is used for KYC and AML routines.
 	 *
-	 * @param string $firstname The end-user's firstname. Useful for some banks
+	 * @param ?string $firstname The end-user's firstname. Useful for some banks
 	 *		for identifying transactions.
 	 *
-	 * @param string $lastname The end-user's lastname. Useful for some banks
+	 * @param ?string $lastname The end-user's lastname. Useful for some banks
 	 *		for identifying transactions.
 	 *
-	 * @param string $nationalidentificationnumber The end-user's social
+	 * @param ?string $nationalidentificationnumber The end-user's social
 	 *		security number / personal number / birth number / etc. Useful for
 	 *		some banks for identifying transactions and KYC/AML.
 	 *
-	 * @param string $shopperstatement The text to show on the end-user's bank
+	 * @param ?string $shopperstatement The text to show on the end-user's bank
 	 *		statement.
 	 *
-	 * @param string $ip The IP-address of the end-user.
+	 * @param ?string $ip The IP-address of the end-user.
 	 *
-	 * @param string $successurl The URL to which the end-user should be
+	 * @param ?string $successurl The URL to which the end-user should be
 	 *		redirected after a successful deposit. Do not put any logic on that
 	 *		page since it's not guaranteed that the end-user will in fact visit
 	 *		it.
 	 *
-	 * @param string $failurl The URL to which the end-user should be
+	 * @param ?string $failurl The URL to which the end-user should be
 	 *		redirected after a failed deposit. Do not put any logic on that
 	 *		page since it's not guaranteed that the end-user will in fact visit
 	 *		it.
 	 *
-	 * @param string $templateurl The URL to your template page for the
+	 * @param ?string $templateurl The URL to your template page for the
 	 *		checkout process.
 	 *
-	 * @param string $urltarget The html target/framename of the SuccessURL.
+	 * @param ?string $urltarget The html target/framename of the SuccessURL.
 	 *		Only _top, _self and _parent are suported.
 	 *
-	 * @param float $suggestedminamount The minimum amount the end-user is
+	 * @param ?float $suggestedminamount The minimum amount the end-user is
 	 *		allowed to deposit in the currency specified by Currency. Only
 	 *		digits. Use dot (.) as decimal separator.
 	 *
-	 * @param float $suggestedmaxamount The maximum amount the end-user is
+	 * @param ?float $suggestedmaxamount The maximum amount the end-user is
 	 *		allowed to deposit in the currency specified by Currency. Only
 	 *		digits. Use dot (.) as decimal separator.
 	 *
-	 * @param string $integrationmodule Version information for your
+	 * @param ?string $integrationmodule Version information for your
 	 *		integration module. This is for informational purposes only and can
 	 *		be useful when troubleshooting problems. Should contain enough
 	 *		version information to be useful.
 	 *
-	 * @param boolean $holdnotifications Do not deliver notifications for this
+	 * @param ?boolean $holdnotifications Do not deliver notifications for this
 	 *		order. This is a parameter available when using test.trustly.com
 	 *		and can be used for manually delivering notifications to your local
 	 *		system during development. Intead you can get you notifications on
 	 *		https://test.trustly.com/notifications.html
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @param mixed $authorizeonly
+	 *
+	 * @param mixed $templatedata
+	 *
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function p2p($notificationurl,$enduserid, $messageid,
 		$locale=NULL, $amount=NULL, $currency=NULL, $country=NULL,
@@ -1115,7 +1125,7 @@ public function p2p($notificationurl,$enduserid, $messageid,
 	 *
 	 * @param integer $currency The currency of the amount
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function capture($orderid, $amount, $currency) {
 
@@ -1142,7 +1152,7 @@ public function capture($orderid, $amount, $currency) {
 	 *
 	 * @param integer $orderid The OrderID of the deposit to void
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function void($orderid) {
 
@@ -1186,10 +1196,10 @@ public function void($orderid) {
 	 * @param string $currency The currency of the end-user's account in the
 	 *		merchant's system.
 	 *
-	 * @param string $shopperstatement The text to show on the end-user's bank
+	 * @param ?string $shopperstatement The text to show on the end-user's bank
 	 *		statement.
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function charge($accountid, $notificationurl, $enduserid, $messageid,
 		$amount, $currency, $shopperstatement=NULL) {
@@ -1220,7 +1230,7 @@ public function charge($accountid, $notificationurl, $enduserid, $messageid,
 	 *
 	 * @param integer $orderid The OrderID of the order to query
 	 *
-	 * @return Trustly_Data_JSONRPCSignedResponse
+	 * @return Trustly_Data_JSONRPCResponse
 	 */
 	public function getWithdrawals($orderid) {
 
diff --git a/Trustly/Api/unsigned.php b/Trustly/Api/unsigned.php
index c62d6b9..def7776 100644
--- a/Trustly/Api/unsigned.php
+++ b/Trustly/Api/unsigned.php
@@ -41,16 +41,16 @@ class Trustly_Api_Unsigned extends Trustly_Api {
 	 * newSessionCookie after which the $session_uuid is used instead.
 	 * @var string
 	 */
-	private $api_username = NULL;
+	private $api_username;
 	/**
 	 * Login password when using the API. Used only in the first API call to
 	 * newSessionCookie after which the $session_uuid is used instead.
 	 * @var string
 	 */
-	private $api_password = NULL;
+	private $api_password;
 	/**
 	 * Session UUID used for authenticating calls.
-	 * @var string
+	 * @var ?string
 	 */
 	private $session_uuid = NULL;
 
@@ -87,7 +87,7 @@ public function __construct($username, $password, $host='trustly.com', $port=443
 	 *
 	 * See specific class implementing the call for more information.
 	 *
-	 * @param Trustly_Data_JSONRPCRequest $request Data to send in the request
+	 * @param ?Trustly_Data_JSONRPCRequest $request Data to send in the request
 	 *
 	 * @return string The URL path
 	 */
@@ -113,7 +113,7 @@ protected function urlPath($request=NULL) {
 	 */
 	protected function handleResponse($request, $body, $response_code) {
 			/* No signature here, just build the response object */
-		return new Trustly_Data_JSONRPCResponse($body, $response_code);
+		return new Trustly_Data_JSONRPCResponse($body);
 	}
 
 
@@ -141,7 +141,7 @@ public function insertCredentials($request) {
 	 * @return boolean indicating wether we have a sessionuuid
 	 */
 	protected function hasSessionUUID() {
-		return (bool)isset($this->session_uuid);
+		return isset($this->session_uuid);
 	}
 
 
@@ -163,10 +163,8 @@ public function newSessionCookie() {
 			 * missing session uuid here and call this function if it is not set */
 		$response = parent::call($request);
 
-		if(isset($response)) {
-			if($response->isSuccess()) {
-				$this->session_uuid = $response->getResult('sessionuuid');
-			}
+		if($response->isSuccess()) {
+			$this->session_uuid = $response->getResult('sessionuuid');
 		}
 		if(!isset($this->session_uuid)) {
 			throw new Trustly_AuthentificationException();
@@ -181,11 +179,11 @@ public function newSessionCookie() {
 	 *
 	 * @param string $viewname Name of view
 	 *
-	 * @param string $dateorder 'OLDER'|'NEVER' or NULL
+	 * @param ?string $dateorder 'OLDER'|'NEVER' or NULL
 	 *
-	 * @param string $datestamp Order used in relation with $dateorder
+	 * @param ?string $datestamp Order used in relation with $dateorder
 	 *
-	 * @param array $filterkeys Array of arrays of filters to apply to the data.
+	 * @param ?array<array<string>> $filterkeys Array of arrays of filters to apply to the data.
 	 *		Arrays in the array consists of 1. Key name, 2. Key value, 3.
 	 *		Operator, 4. Key value 2. Operator is one of 'NOT', 'BETWEEN' (in
 	 *		which case Key value 2 must be set), 'LIKE', 'DECRYPTED', 'IN'
@@ -195,11 +193,11 @@ public function newSessionCookie() {
 	 *
 	 * @param integer $offset Skip these many records in the start of the request
 	 *
-	 * @param string $params Parameters for the view
+	 * @param ?string $params Parameters for the view
 	 *
-	 * @param string $sortby Column to sort by
+	 * @param ?string $sortby Column to sort by
 	 *
-	 * @param string $sortorder Sort order ASC or DESC
+	 * @param ?string $sortorder Sort order ASC or DESC
 	 *
 	 * @return Trustly_Data_JSONRPCResponse Response from the API.
 	 *
@@ -208,7 +206,8 @@ public function getViewStable($viewname, $dateorder=NULL, $datestamp=NULL,
 		$filterkeys=NULL, $limit=100, $offset=0, $params=NULL, $sortby=NULL,
 		$sortorder=NULL) {
 
-		return $this->call('GetViewStable', array(
+		$request = new Trustly_Data_JSONRPCRequest('GetViewStable');
+		return $this->call($request, array(
 			'DateOrder' => $dateorder,
 			'Datestamp' => $datestamp,
 			'FilterKeys' => $filterkeys,
@@ -229,15 +228,13 @@ public function getViewStable($viewname, $dateorder=NULL, $datestamp=NULL,
 	 * the outgoing call. Take care when supplying the arguments for the call
 	 * so they match the function prototype properly.
 	 *
-	 * @param string $method API method to call
+	 * @param Trustly_Data_JSONRPCRequest $request Outgoing request
 	 *
-	 * @param Trustly_Data_JSONRPCRequest $params Outgoing call params
+	 * @param ?array<string, mixed> $params Outgoing call params
 	 *
 	 * @return Trustly_Data_JSONRPCResponse Response from the API.
 	 */
-	public function call($method, $params=NULL)  {
-		$request = new Trustly_Data_JSONRPCRequest($method);
-
+	public function call($request, $params=NULL) {
 		if(isset($params)) {
 			foreach($params as $key => $value) {
 				$request->setParam($key, $value);
diff --git a/Trustly/Data/data.php b/Trustly/Data/data.php
index a77274b..df0c510 100644
--- a/Trustly/Data/data.php
+++ b/Trustly/Data/data.php
@@ -37,26 +37,18 @@
 class Trustly_Data {
 	/**
 	 * Data payload
-	 * @var array
+	 * @var array<mixed>
 	 */
-	protected $payload = NULL;
-
-	/**
-	 * Constructur.
-	 */
-	public function __construct() {
-		$this->payload = array();
-	}
-
+	protected $payload = array();
 
 	/**
 	 * Utility function to vacuum the supplied data end remove unset
 	 * values. This is used to keep the requests cleaner rather then
 	 * supplying NULL values in the payload
 	 *
-	 * @param array $data data to clean
+	 * @param mixed $data data to clean
 	 *
-	 * @return array cleaned data
+	 * @return mixed cleaned data
 	 */
 	public function vacuum($data) {
 		if(is_null($data)) {
@@ -83,7 +75,7 @@ public function vacuum($data) {
 	 * Get the specific data value from the payload or the full payload if
 	 * no value is supplied
 	 *
-	 * @param string $name The optional data parameter to get. If NULL then the
+	 * @param ?string $name The optional data parameter to get. If NULL then the
 	 * entire payload will be returned.
 	 *
 	 * @return mixed value
@@ -106,7 +98,7 @@ public function get($name=NULL) {
 	 *
 	 * @param string $str String to process
 	 *
-	 * @return string UTF-8 variant of string
+	 * @return ?string UTF-8 variant of string
 	 */
 	public static function ensureUTF8($str) {
 		if($str == NULL) {
@@ -128,6 +120,8 @@ public static function ensureUTF8($str) {
 	 * @param string $name
 	 *
 	 * @param mixed $value
+	 *
+	 * @return void
 	 */
 	public function set($name, $value) {
 		$this->payload[$name] = Trustly_Data::ensureUTF8($value);
@@ -158,7 +152,7 @@ public function pop($name) {
 	 * @param boolean $pretty Format the output in a prettified easy-to-read
 	 *		formatting
 	 *
-	 * @return string The current payload in JSON
+	 * @return string|false The current payload in JSON
 	 */
 	public function json($pretty=FALSE) {
 		if($pretty) {
@@ -179,7 +173,9 @@ public function json($pretty=FALSE) {
 	 * pretty printer
 	 *
 	 * @param mixed $data Payload to sort. Will be sorted in place
-	 * */
+	 *
+	 * @return void
+	 */
 	private function sortRecursive(&$data) {
 		if(is_array($data)) {
 			foreach($data as $k => $v) {
diff --git a/Trustly/Data/jsonrpcnotificationrequest.php b/Trustly/Data/jsonrpcnotificationrequest.php
index 6be3c5f..4134ab5 100644
--- a/Trustly/Data/jsonrpcnotificationrequest.php
+++ b/Trustly/Data/jsonrpcnotificationrequest.php
@@ -40,7 +40,7 @@ class Trustly_Data_JSONRPCNotificationRequest extends Trustly_Data {
 	 * The RAW incoming notification body
 	 * @var string
 	 */
-	var $notification_body = NULL;
+	public $notification_body;
 
 
 	/**
@@ -52,11 +52,9 @@ class Trustly_Data_JSONRPCNotificationRequest extends Trustly_Data {
 	 *		request seems to be valid but is for a JSON RPC version we do not
 	 *		support.
 	 *
-	 * @param string $notification RAW incoming notification body
+	 * @param string $notification_body RAW incoming notification body
 	 */
 	public function __construct($notification_body) {
-		parent::__construct();
-
 		$this->notification_body = $notification_body;
 
 		if(empty($notification_body)) {
@@ -84,7 +82,7 @@ public function __construct($notification_body) {
 	/**
 	 * Get value from or the entire params payload.
 	 *
-	 * @param string $name Name of the params parameter to obtain. Leave blank
+	 * @param ?string $name Name of the params parameter to obtain. Leave blank
 	 *		to get the entire payload
 	 *
 	 * @return mixed The value for the params parameter or the entire payload
@@ -110,7 +108,7 @@ public function getParams($name=NULL) {
 	 * Get the value of a parameter in the params->data section of the
 	 * notification response.
 	 *
-	 * @param string $name The name of the parameter. Leave as NULL to get the
+	 * @param ?string $name The name of the parameter. Leave as NULL to get the
 	 *		entire payload.
 	 *
 	 * @return mixed The value sought after or the entire payload depending on
@@ -135,7 +133,7 @@ public function getData($name=NULL) {
 	/**
 	 * Get the UUID from the request.
 	 *
-	 * @return string The UUID value
+	 * @return ?string The UUID value
 	 */
 	public function getUUID() {
 		return $this->getParams('uuid');
@@ -145,7 +143,7 @@ public function getUUID() {
 	/**
 	 * Get the Method from the request.
 	 *
-	 * @return string The Method value.
+	 * @return ?string The Method value.
 	 */
 	public function getMethod() {
 		return $this->get('method');
@@ -155,7 +153,7 @@ public function getMethod() {
 	/**
 	 * Get the Signature from the request.
 	 *
-	 * @return string The Signature value.
+	 * @return ?string The Signature value.
 	 */
 	public function getSignature() {
 		return $this->getParams('signature');
@@ -165,7 +163,7 @@ public function getSignature() {
 	/**
 	 * Get the JSON RPC version from the request.
 	 *
-	 * @return string The Version.
+	 * @return ?string The Version.
 	 */
 	public function getVersion() {
 		return $this->get('version');
diff --git a/Trustly/Data/jsonrpcnotificationresponse.php b/Trustly/Data/jsonrpcnotificationresponse.php
index 87894a8..57d4afe 100644
--- a/Trustly/Data/jsonrpcnotificationresponse.php
+++ b/Trustly/Data/jsonrpcnotificationresponse.php
@@ -42,13 +42,10 @@ class Trustly_Data_JSONRPCNotificationResponse extends Trustly_Data {
 	 * @param Trustly_Data_JSONRPCNotificationRequest $request Incoming
 	 *		notification request to which we are responding
 	 *
-	 * @param boolean $success Set to true to indicate that the notification
+	 * @param ?boolean $success Set to true to indicate that the notification
 	 *		was successfully processed.
 	 */
 	public function __construct($request, $success=NULL) {
-
-		parent::__construct();
-
 		$uuid = $request->getUUID();
 		$method = $request->getMethod();
 
@@ -70,10 +67,10 @@ public function __construct($request, $success=NULL) {
 	/**
 	 * Set the success status in the response.
 	 *
-	 * @param boolean $success Set to true to indicate that the notification
+	 * @param ?boolean $success Set to true to indicate that the notification
 	 *		was successfully processed.
 	 *
-	 * @return $success
+	 * @return ?boolean $success
 	 */
 	public function setSuccess($success=NULL) {
 		$status = 'OK';
@@ -91,7 +88,7 @@ public function setSuccess($success=NULL) {
 	 *
 	 * @param string $signature Signature of the outgoing data.
 	 *
-	 * @return string $signature
+	 * @return void
 	 */
 	public function setSignature($signature) {
 		$this->setResult('signature', $signature);
@@ -120,7 +117,7 @@ public function setResult($name, $value) {
 	 * Get the value of a parameter in the result section of the notification
 	 * response.
 	 *
-	 * @param string $name The name of the parameter. Leave as NULL to get the
+	 * @param ?string $name The name of the parameter. Leave as NULL to get the
 	 *		entire payload.
 	 *
 	 * @return mixed The value sought after or the entire payload depending on
@@ -148,7 +145,7 @@ public function getResult($name=NULL) {
 	 * Get the value of a parameter in the result->data section of the
 	 * notification response.
 	 *
-	 * @param string $name The name of the parameter. Leave as NULL to get the
+	 * @param ?string $name The name of the parameter. Leave as NULL to get the
 	 *		entire payload.
 	 *
 	 * @return mixed The value sought after or the entire payload depending on
@@ -198,7 +195,7 @@ public function setData($name, $value) {
 	/**
 	 * Get the Method value from the response.
 	 *
-	 * @return string The Method value.
+	 * @return ?string The Method value.
 	 */
 	public function getMethod() {
 		return $this->getResult('method');
@@ -208,7 +205,7 @@ public function getMethod() {
 	/**
 	 * Get the UUID value from the response.
 	 *
-	 * @return string The UUID value
+	 * @return ?string The UUID value
 	 */
 	public function getUUID() {
 		return $this->getResult('uuid');
diff --git a/Trustly/Data/jsonrpcrequest.php b/Trustly/Data/jsonrpcrequest.php
index 2b10f9a..57c481e 100644
--- a/Trustly/Data/jsonrpcrequest.php
+++ b/Trustly/Data/jsonrpcrequest.php
@@ -41,7 +41,7 @@ class Trustly_Data_JSONRPCRequest extends Trustly_Data_Request {
 	 * @throws Trustly_DataException If the combination of $data and
 	 *		$attributes is invalid
 	 *
-	 * @param string $method Outgoing call API method
+	 * @param ?string $method Outgoing call API method
 	 *
 	 * @param mixed $data Outputgoing call Data (if any). This can be either an
 	 *		array or a simple non-complex value.
@@ -149,7 +149,7 @@ public function setUUID($uuid) {
 	/**
 	 * Get the UUID value from the outgoing call.
 	 *
-	 * @return string The UUID value
+	 * @return ?string The UUID value
 	 */
 	public function getUUID() {
 		if(isset($this->payload['params']['UUID'])) {
@@ -163,17 +163,17 @@ public function getUUID() {
 	 *
 	 * @param string $method The name of the API method this call is for
 	 *
-	 * @return string $method
+	 * @return void
 	 */
 	public function setMethod($method) {
-		return $this->set('method', $method);
+		$this->set('method', $method);
 	}
 
 
 	/**
 	 * Get the Method value from the outgoing call.
 	 *
-	 * @return string The Method value.
+	 * @return ?string The Method value.
 	 */
 	public function getMethod() {
 		return $this->get('method');
@@ -202,7 +202,7 @@ public function setData($name, $value) {
 	 * Get the value of one parameter in the params->Data section of the
 	 * request. Or the entire Data section if no name is given.
 	 *
-	 * @param string $name Name of the Data param to obtain. Leave as NULL to
+	 * @param ?string $name Name of the Data param to obtain. Leave as NULL to
 	 *		get the entire structure.
 	 *
 	 * @return mixed The value or the entire Data depending on $name
diff --git a/Trustly/Data/jsonrpcresponse.php b/Trustly/Data/jsonrpcresponse.php
index 98a2c4c..a53a72e 100644
--- a/Trustly/Data/jsonrpcresponse.php
+++ b/Trustly/Data/jsonrpcresponse.php
@@ -78,7 +78,7 @@ public function __construct($response_body) {
 	/**
 	 * Get error code (if any) from the API response
 	 *
-	 * @return integer The error code (numerical)
+	 * @return ?integer The error code (numerical)
 	 */
 	public function getErrorCode() {
 		if($this->isError() && isset($this->response_result['code'])) {
@@ -90,7 +90,7 @@ public function getErrorCode() {
 	/**
 	 * Get error message (if any) from the API response
 	 *
-	 * @return string The error message
+	 * @return ?string The error message
 	 */
 	public function getErrorMessage() {
 		if($this->isError() && isset($this->response_result['message'])) {
diff --git a/Trustly/Data/jsonrpcsignedresponse.php b/Trustly/Data/jsonrpcsignedresponse.php
index 4b16b02..5ff0d1d 100644
--- a/Trustly/Data/jsonrpcsignedresponse.php
+++ b/Trustly/Data/jsonrpcsignedresponse.php
@@ -88,7 +88,7 @@ public function __construct($response_body) {
 	/**
 	 * Get data from the data section of the response
 	 *
-	 * @param string $name Name of the data parameter to fetch. NULL value will
+	 * @param ?string $name Name of the data parameter to fetch. NULL value will
 	 *		return entire data section.
 	 *
 	 * @return mixed The value for parameter $name or the entire data block if
@@ -116,7 +116,7 @@ public function getData($name=NULL) {
 	/**
 	 * Get error code (if any) from the API call
 	 *
-	 * @return integer The error code (numerical)
+	 * @return ?integer The error code (numerical)
 	 */
 	public function getErrorCode() {
 		if($this->isError() && isset($this->response_result['data']['code'])) {
@@ -129,7 +129,7 @@ public function getErrorCode() {
 	/**
 	 * Get error message (if any) from the API call
 	 *
-	 * @return string The error message
+	 * @return ?string The error message
 	 */
 	public function getErrorMessage() {
 		if($this->isError() && isset($this->response_result['data']['message'])) {
diff --git a/Trustly/Data/request.php b/Trustly/Data/request.php
index 3daaca7..817b91f 100644
--- a/Trustly/Data/request.php
+++ b/Trustly/Data/request.php
@@ -36,20 +36,18 @@
 class Trustly_Data_Request extends Trustly_Data {
 	/**
 	 * Call method name
-	 * @var string
+	 * @var ?string
 	 */
-	var $method = NULL;
+	public $method = NULL;
 
 	/**
 	 * Constructor.
 	 *
-	 * @param string $method Method name for the call
+	 * @param ?string $method Method name for the call
 	 *
-	 * @param array $payload Call payload
+	 * @param ?array<mixed> $payload Call payload
 	 */
 	public function __construct($method=NULL, $payload=NULL) {
-		parent::__construct();
-
 		$vpayload = $this->vacuum($payload);
 		if(isset($vpayload)) {
 			$this->payload = $vpayload;
@@ -62,7 +60,7 @@ public function __construct($method=NULL, $payload=NULL) {
 	/**
 	 * Convenience function for getting the uuid from the call
 	 *
-	 * @return string uuid
+	 * @return ?string uuid
 	 */
 	public function getUUID() {
 		if(isset($this->payload['uuid'])) {
@@ -75,7 +73,9 @@ public function getUUID() {
 	/**
 	 * Convenience function for setting the uuid in the call
 	 *
-	 * @param string uuid
+	 * @param string $uuid
+	 *
+	 * @return void
 	 */
 	public function setUUID($uuid) {
 		$this->set('uuid', $uuid);
@@ -85,7 +85,7 @@ public function setUUID($uuid) {
 	/**
 	 * Get the method in the outgoing call
 	 *
-	 * @return string method name
+	 * @return ?string method name
 	 */
 	public function getMethod() {
 		return $this->method;
@@ -95,7 +95,9 @@ public function getMethod() {
 	/**
 	 * Set the medhod in the call
 	 *
-	 * @param string method name
+	 * @param string $method method name
+	 *
+	 * @return void
 	 */
 	public function setMethod($method) {
 		$this->method = $method;
diff --git a/Trustly/Data/response.php b/Trustly/Data/response.php
index 0f4b97b..a19ab85 100644
--- a/Trustly/Data/response.php
+++ b/Trustly/Data/response.php
@@ -37,21 +37,21 @@ class Trustly_Data_Response extends Trustly_Data {
 
 	/**
 	 * Raw copy of the incoming response body
-	 * @var integer
+	 * @var ?string
 	 */
-	var $response_body = NULL;
+	public $response_body = NULL;
 
 	/**
 	 * The response HTTP code
-	 * @var integer
+	 * @var ?integer
 	 */
-	var $response_code = NULL;
+	public $response_code = NULL;
 
 	/**
 	 * Shortcut to the part of the result being actually interesting. The guts will contain all returned data.
 	 * @var mixed
 	 */
-	var $response_result = NULL;
+	public $response_result = NULL;
 
 
 	/**
@@ -64,11 +64,9 @@ class Trustly_Data_Response extends Trustly_Data {
 	 *
 	 * @param string $response_body RAW response body from the API call
 	 *
-	 * @param integer $response_code HTTP response code from the API call
+	 * @param ?integer $response_code HTTP response code from the API call
 	 */
 	public function __construct($response_body, $response_code=NULL) {
-		parent::__construct();
-
 		$this->response_code = $response_code;
 		$this->response_body = $response_body;
 
@@ -135,7 +133,7 @@ public function isSuccess() {
 	/**
 	 * Get error message (if any) from the API response
 	 *
-	 * @return string The error message
+	 * @return ?string The error message
 	 */
 	public function getErrorMessage() {
 		if($this->isError()) {
@@ -150,7 +148,7 @@ public function getErrorMessage() {
 	/**
 	 * Get error code (if any) from the API response
 	 *
-	 * @return integer The error code (numerical)
+	 * @return ?integer The error code (numerical)
 	 */
 	public function getErrorCode() {
 		if($this->isError()) {
@@ -165,7 +163,7 @@ public function getErrorCode() {
 	/**
 	 * Get data from the result section of the response
 	 *
-	 * @param string $name Name of the result parameter to fetch. NULL value
+	 * @param ?string $name Name of the result parameter to fetch. NULL value
 	 *		will return entire result section.
 	 *
 	 * @return mixed The value for parameter $name or the entire result block
@@ -188,7 +186,7 @@ public function getResult($name=NULL) {
 	/**
 	 * Convenience function for getting the uuid in the response
 	 *
-	 * @param string uuid
+	 * @return ?string uuid
 	 */
 	public function getUUID() {
 		if(isset($this->response_result['uuid'])) {
@@ -201,7 +199,7 @@ public function getUUID() {
 	/**
 	 * Get the method from the response
 	 *
-	 * @return string method name
+	 * @return ?string method name
 	 */
 	public function getMethod() {
 		if(isset($this->response_result['method'])) {
@@ -214,7 +212,7 @@ public function getMethod() {
 	/**
 	 * Get the signature from the response
 	 *
-	 * @return string signature
+	 * @return ?string signature
 	 */
 	public function getSignature() {
 		if(isset($this->response_result['signature'])) {
diff --git a/Trustly/exceptions.php b/Trustly/exceptions.php
index e1a9724..f4fa489 100644
--- a/Trustly/exceptions.php
+++ b/Trustly/exceptions.php
@@ -47,13 +47,15 @@ class Trustly_JSONRPCVersionException extends Exception { }
  * indication that message contents are being tampered with.
  */
 class Trustly_SignatureException extends Exception {
+	/** @var mixed */
+	public $signature_data = NULL;
 
 	/**
 	 * Constructor
 	 *
 	 * @param string $message Exception message
 	 *
-	 * @param array $data Data that was signed with an invalid signature
+	 * @param mixed $data Data that was signed with an invalid signature
 	 */
 	public function __construct($message, $data=NULL) {
 		parent::__construct($message);
@@ -65,6 +67,8 @@ public function __construct($message, $data=NULL) {
 	 * Get the data that had an invalid signature. This is the only way to get
 	 * data from anything with a bad signature. This should be used for
 	 * DEBUGGING ONLY. You should NEVER rely on the contents.
+	 *
+	 * @return mixed
 	 */
 	public function getBadData() {
 		return $this->signature_data;
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..85237fc
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,4 @@
+parameters:
+    level: 8
+    paths:
+        - ./Trustly/