diff --git a/README.md b/README.md
index 45c7e6e..045c51b 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,23 @@
 [![](https://img.shields.io/badge/version-0.0.1-blue.svg)](https://shields.io/)
 [![](https://img.shields.io/badge/maintained-yes-green.svg)](https://shields.io/)
 
-## Quick start
+PHP package for Croatian fiscalization. 
+
+
+## Install the packages
 
 - `composer install`
+
+
+## Update required fields in tests
+
+In order for tests to work, head to `tests\CroatianFiscalizationTest` and change the required fields which you will need to have in order for fiscalization to work:
+
+- Test certificate with path and password
+- Company UID
+- Operative user UID
+
+
+## Run the tests
+
 - `php vendor/phpunit/phpunit/phpunit`
\ No newline at end of file
diff --git a/composer.json b/composer.json
index ca00ce8..8d23c55 100644
--- a/composer.json
+++ b/composer.json
@@ -6,7 +6,12 @@
     ],
     "type": "library",
     "require": {
-        "php": "^7.4"
+        "php": "^7.4",
+        "ext-xmlwriter": "*",
+        "ext-openssl": "*",
+        "ext-dom": "*",
+        "ext-curl": "*",
+        "ext-simplexml": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "^8.5"
diff --git a/src/Bill/Bill.php b/src/Bill/Bill.php
deleted file mode 100644
index 5573bf6..0000000
--- a/src/Bill/Bill.php
+++ /dev/null
@@ -1,8 +0,0 @@
-<?php
-
-namespace src\Bill;
-
-class Bill
-{
-
-}
diff --git a/src/Bill/BillNumber.php b/src/Bill/BillNumber.php
deleted file mode 100644
index 06985f6..0000000
--- a/src/Bill/BillNumber.php
+++ /dev/null
@@ -1,8 +0,0 @@
-<?php
-
-namespace src\Bill;
-
-class BillNumber
-{
-
-}
\ No newline at end of file
diff --git a/src/Bill/BillRequest.php b/src/Bill/BillRequest.php
deleted file mode 100644
index 846e2af..0000000
--- a/src/Bill/BillRequest.php
+++ /dev/null
@@ -1,8 +0,0 @@
-<?php
-
-namespace src\Bill;
-
-class BillRequest
-{
-
-}
\ No newline at end of file
diff --git a/src/Bill/TaxRate.php b/src/Bill/TaxRate.php
deleted file mode 100644
index 58642f4..0000000
--- a/src/Bill/TaxRate.php
+++ /dev/null
@@ -1,8 +0,0 @@
-<?php
-
-namespace src\Bill;
-
-class TaxRate
-{
-
-}
\ No newline at end of file
diff --git a/src/Company/Certificate.php b/src/Company/Certificate.php
new file mode 100644
index 0000000..b3cf42e
--- /dev/null
+++ b/src/Company/Certificate.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace tonikresic\CroatianFiscalization\Company;
+
+class Certificate
+{
+    /**
+     * Path to the Certificate.
+     *
+     * @var string
+     */
+    public string $path;
+
+    /**
+     * Certificate password.
+     *
+     * @var string
+     */
+    public string $password;
+
+    /**
+     * Certificate constructor.
+     *
+     * @param string $path
+     * @param string $password
+     */
+    public function __construct(string $path, string $password)
+    {
+        $this->path = $path;
+        $this->password = $password;
+    }
+}
\ No newline at end of file
diff --git a/src/Company/Company.php b/src/Company/Company.php
new file mode 100644
index 0000000..f367e9b
--- /dev/null
+++ b/src/Company/Company.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace tonikresic\CroatianFiscalization\Company;
+
+class Company
+{
+    /**
+     * Company UID.
+     *
+     * @var string
+     */
+    public string $uid;
+
+    /**
+     * Company fiscalization Certificate.
+     *
+     * @var Certificate
+     */
+    public Certificate $certificate;
+
+    /**
+     * Demo fiscalization.
+     *
+     * @var bool
+     */
+    public bool $demo;
+
+
+    /**
+     * If the Invoice should be taxed.
+     *
+     * @var bool
+     */
+    public bool $shouldBeTaxed;
+
+    /**
+     * Company constructor.
+     *
+     * @param string $uid
+     * @param Certificate $certificate
+     * @param bool $demo
+     * @param bool $shouldBeTaxed
+     */
+    public function __construct(string $uid, Certificate $certificate, bool $demo, bool $shouldBeTaxed)
+    {
+        $this->uid = $uid;
+        $this->certificate = $certificate;
+        $this->demo = $demo;
+        $this->shouldBeTaxed = $shouldBeTaxed;
+    }
+}
\ No newline at end of file
diff --git a/src/CroatianFiscalization.php b/src/CroatianFiscalization.php
index 116a06e..17782f0 100644
--- a/src/CroatianFiscalization.php
+++ b/src/CroatianFiscalization.php
@@ -1,12 +1,479 @@
 <?php
 
-namespace src\CroatianFiscalization;
+namespace tonikresic\CroatianFiscalization;
 
-use src\Bill\Bill;
-use src\Bill\BillNumber;
+use DOMDocument;
+use DOMElement;
+use Exception;
+use tonikresic\CroatianFiscalization\Company\Company;
+use tonikresic\CroatianFiscalization\Invoice\Invoice;
+use tonikresic\CroatianFiscalization\Invoice\InvoiceNumber;
+use tonikresic\CroatianFiscalization\Invoice\InvoiceRequest;
+use tonikresic\CroatianFiscalization\Invoice\TaxRate;
 
 class CroatianFiscalization
 {
-    private Bill $bill;
-    private BillNumber $billNumber;
-}
\ No newline at end of file
+    /**
+     * Company.
+     *
+     * @var Company
+     */
+    private Company $company;
+
+    /**
+     * Invoice number.
+     *
+     * @var InvoiceNumber
+     */
+    private InvoiceNumber $invoiceNumber;
+
+    /**
+     * Certificate data.
+     *
+     * @var array|null
+     */
+    private ?array $certificate;
+
+
+    /**
+     * Security protocol.
+     *
+     * @var string
+     */
+    private string $security = 'TLS';
+
+    /**
+     * Private key resource.
+     *
+     * @var
+     */
+    private $privateKeyResource;
+
+    /**
+     * Certificate data.
+     *
+     * @var array
+     */
+    private array $publicCertificateData;
+
+    /**
+     * Croatian fiscalization Demo API URL. The real URL is commented out and requires real certificate in order to work.
+     *
+     * @var string
+     */
+    private string $url = 'https://cistest.apis-it.hr:8449/FiskalizacijaServiceTest'; //'https://cis.porezna-uprava.hr:8449/FiskalizacijaService';
+
+    /**
+     * Demo fiscalization.
+     *
+     * @var bool
+     */
+    private bool $demo = true;
+
+    /**
+     * Configures fiscalization data.
+     *
+     * @param Company $company
+     */
+    public function configure(Company $company)
+    {
+        $this->company = $company;
+
+        if ($this->company->demo) {
+            $this->url = 'https://cistest.apis-it.hr:8449/FiskalizacijaServiceTest';
+        }
+
+        try {
+            $this->setCertificate($company->certificate->path, $company->certificate->password);
+        } catch (Exception $e) {
+            fwrite(STDERR, print_r('An exception happened: ' . $e->getMessage(), TRUE));
+        }
+    }
+
+    /**
+     * Validates required attributes.
+     *
+     * @param object $invoiceObject
+     * @return object
+     */
+    protected function validate(object $invoiceObject): object
+    {
+
+        if (!isset($invoiceObject->userUID) || empty($invoiceObject->userUID)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice user UID is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->company) || empty($invoiceObject->company)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice company is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->fiscal_data) || empty($invoiceObject->fiscal_data)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice fiscal data is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->fiscal_abbreviation) || empty($invoiceObject->fiscal_abbreviation)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Fiscal abbreviation is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->gross) || empty($invoiceObject->gross)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice gross is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->net) || empty($invoiceObject->net)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice net is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->number) || empty($invoiceObject->number)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice number is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->business_place_label) || empty($invoiceObject->business_place_label)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice business place label is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->cash_register_label) || empty($invoiceObject->cash_register_label)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice cash register label is required.'
+            ];
+        }
+
+        if (!isset($invoiceObject->created_at) || empty($invoiceObject->created_at)) {
+            return (object) [
+                'success' => false,
+                'message' => 'Invoice created at field is required.'
+            ];
+        }
+
+        return (object) [
+            'success' => true,
+            'message' => NULL
+        ];
+    }
+
+    /**
+     * Fiscalizes the given Invoice.
+     *
+     * @param object $invoiceObject
+     * @return object
+     * @throws Exception
+     */
+    public function fiscalize(object $invoiceObject): object
+    {
+        $validation = $this->validate($invoiceObject);
+
+        if (!$validation->success) {
+            return (object) [
+                'success' => $validation->success,
+                'message' => $validation->message
+            ];
+        }
+
+        $this->createInvoiceNumber($invoiceObject);
+
+        $fiscalizedInvoice = $this->createFiscalizedInvoice($invoiceObject);
+
+        if ($invoiceObject->fiscal_data && $invoiceObject->fiscal_data->zki) {
+            $fiscalizedInvoice->setSecurityCode($invoiceObject->fiscal_data->zki);
+            $fiscalizedInvoice->setNoteOfRedelivery(true);
+        } else {
+            $fiscalizedInvoice->setSecurityCode(
+                $fiscalizedInvoice->formatSecurityCode(
+                    $this->certificate['pkey'],
+                    $fiscalizedInvoice->uid,
+                    $fiscalizedInvoice->dateTime,
+                    $this->invoiceNumber->numberNoteInvoice,
+                    $this->invoiceNumber->noteOfBusinessArea,
+                    $this->invoiceNumber->noteOfExchangeDevice,
+                    $fiscalizedInvoice->totalValue
+                )
+            );
+            $fiscalizedInvoice->setNoteOfRedelivery(false);
+            $fiscalizedInvoice->zki = $fiscalizedInvoice->securityCode;
+        }
+
+        $invoice_request = new InvoiceRequest($fiscalizedInvoice);
+        try {
+            $soapMessage = $this->signXML($invoice_request->toXML());
+            $res = $this->sendSoap($soapMessage);
+
+            $cleanXML = str_ireplace(['SOAP-ENV:', 'SOAP:', 'tns:'], '', $res);
+            $response = simplexml_load_string($cleanXML);
+
+            if ($response->Body->RacunOdgovor->Greske) {
+                $error = $response->Body->RacunOdgovor->Greske->Greska;
+                return (object) [
+                    'success' => false,
+                    'message' => "An error occurred with message: {$error->SifraGreske}: {$error->PorukaGreske}"
+                ];
+            }
+
+            $jir = (string) $response->Body->RacunOdgovor->Jir;
+            $date = (string) $response->Body->RacunOdgovor->Zaglavlje->DatumVrijeme;
+
+            return (object) [
+                'success' => true,
+                'zki' => $fiscalizedInvoice->zki,
+                'jir' => $jir,
+                'fiscal_at' => \DateTime::createFromFormat('d.m.Y\TH:i:s', $date)->format('Y-m-d H:i:s')
+            ];
+        } catch (\Exception $e) {
+            return (object) [
+                'success' => false,
+                'message' => 'An exception occurred with message: ' . $e->getMessage()
+            ];
+        }
+    }
+
+    /**
+     * Creates InvoiceNumber from Invoice data.
+     *
+     * @param object $invoiceObject
+     */
+    public function createInvoiceNumber(object $invoiceObject): void
+    {
+        $this->invoiceNumber = new InvoiceNumber(
+            $invoiceObject->number,
+            $invoiceObject->business_place_label,
+            $invoiceObject->cash_register_label
+        );
+    }
+
+    /**
+     * Creates instance of a Invoice class for further fiscalization.
+     *
+     * @param object $invoiceObject
+     * @return Invoice
+     */
+    public function createFiscalizedInvoice(object $invoiceObject): Invoice
+    {
+        $billedAt = \DateTime::createFromFormat('Y-m-d H:i:s', $invoiceObject->created_at)->format('d.m.Y\TH:i:s');
+        $fiscalizedInvoice = new Invoice();
+        $fiscalizedInvoice->setUID($this->company->uid);
+        $fiscalizedInvoice->setHaveTax($this->company->shouldBeTaxed);
+        $fiscalizedInvoice->setInvoiceNumber($this->invoiceNumber);
+        $fiscalizedInvoice->setNoteOfOrder('P');
+        $fiscalizedInvoice->setDateTime($billedAt);
+        $taxRate = $this->company->shouldBeTaxed ? (100 * ($invoiceObject->gross / $invoiceObject->net - 1.0)) : 0;
+        $fiscalizedInvoice->setListTax([
+            new TaxRate(round($taxRate, 2), $invoiceObject->net, ($invoiceObject->gross - $invoiceObject->net), null)
+        ]);
+        $fiscalizedInvoice->setTotalValue($invoiceObject->gross);
+        $fiscalizedInvoice->setTypeOfPayment($invoiceObject->fiscal_abbreviation);
+        $fiscalizedInvoice->setOperativeUID($invoiceObject->userUID);
+
+        return $fiscalizedInvoice;
+    }
+
+    /**
+     * Sets certificate data.
+     *
+     * @param $path
+     * @param $pass
+     * @throws Exception
+     */
+    public function setCertificate($path, $pass)
+    {
+        $pkcs12 = $this->getCertificate($path);
+        openssl_pkcs12_read($pkcs12, $this->certificate, $pass);
+        $this->privateKeyResource = openssl_pkey_get_private($this->certificate['pkey'], $pass);
+        $this->publicCertificateData = openssl_x509_parse($this->certificate['cert']);
+    }
+
+    /**
+     * Get certificate.
+     *
+     * @param $path
+     * @return false|string
+     * @throws Exception
+     */
+    public function getCertificate($path)
+    {
+        if (!$cert = @file_get_contents($path)) {
+            throw new \Exception('Cannot read certificate from location: ' . $path, 1);
+        }
+        return $cert;
+    }
+
+    /**
+     * Constructs SOAP message.
+     *
+     * @param $XMLRequest
+     * @return string
+     * @throws Exception
+     */
+    public function signXML($XMLRequest)
+    {
+        $XMLRequestDOMDoc = new DOMDocument();
+        $XMLRequestDOMDoc->loadXML($XMLRequest);
+
+        $canonical = $XMLRequestDOMDoc->C14N();
+        $DigestValue = base64_encode(hash('sha1', $canonical, true));
+
+        $rootElem = $XMLRequestDOMDoc->documentElement;
+
+        $SignatureNode = $rootElem->appendChild(new DOMElement('Signature'));
+        $SignatureNode->setAttribute('xmlns', 'http://www.w3.org/2000/09/xmldsig#');
+
+        $SignedInfoNode = $SignatureNode->appendChild(new DOMElement('SignedInfo'));
+        $SignedInfoNode->setAttribute('xmlns', 'http://www.w3.org/2000/09/xmldsig#');
+
+        $CanonicalizationMethodNode = $SignedInfoNode->appendChild(new DOMElement('CanonicalizationMethod'));
+        $CanonicalizationMethodNode->setAttribute('Algorithm', 'http://www.w3.org/2001/10/xml-exc-c14n#');
+
+        $SignatureMethodNode = $SignedInfoNode->appendChild(new DOMElement('SignatureMethod'));
+        $SignatureMethodNode->setAttribute('Algorithm', 'http://www.w3.org/2000/09/xmldsig#rsa-sha1');
+
+        $ReferenceNode = $SignedInfoNode->appendChild(new DOMElement('Reference'));
+        $ReferenceNode->setAttribute('URI', sprintf('#%s', $XMLRequestDOMDoc->documentElement->getAttribute('Id')));
+
+        $TransformsNode = $ReferenceNode->appendChild(new DOMElement('Transforms'));
+
+        $Transform1Node = $TransformsNode->appendChild(new DOMElement('Transform'));
+        $Transform1Node->setAttribute('Algorithm', 'http://www.w3.org/2000/09/xmldsig#enveloped-signature');
+
+        $Transform2Node = $TransformsNode->appendChild(new DOMElement('Transform'));
+        $Transform2Node->setAttribute('Algorithm', 'http://www.w3.org/2001/10/xml-exc-c14n#');
+
+        $DigestMethodNode = $ReferenceNode->appendChild(new DOMElement('DigestMethod'));
+        $DigestMethodNode->setAttribute('Algorithm', 'http://www.w3.org/2000/09/xmldsig#sha1');
+
+        $ReferenceNode->appendChild(new DOMElement('DigestValue', $DigestValue));
+
+        $SignedInfoNode = $XMLRequestDOMDoc->getElementsByTagName('SignedInfo')->item(0);
+
+        $X509Issuer = $this->publicCertificateData['issuer'];
+        $X509IssuerName = sprintf('O=%s,C=%s', $X509Issuer['O'], $X509Issuer['C']);
+        $X509IssuerSerial = $this->publicCertificateData['serialNumber'];
+
+        $publicCertificatePureString = str_replace('-----BEGIN CERTIFICATE-----', '', $this->certificate['cert']);
+        $publicCertificatePureString = str_replace('-----END CERTIFICATE-----', '', $publicCertificatePureString);
+
+        $signedInfoSignature = null;
+
+        if (!openssl_sign($SignedInfoNode->C14N(true), $signedInfoSignature, $this->privateKeyResource, OPENSSL_ALGO_SHA1))
+            throw new Exception('Unable to sign the SOAP request for CroatianFiscalization.');
+
+        $SignatureNode = $XMLRequestDOMDoc->getElementsByTagName('Signature')->item(0);
+        $SignatureValueNode = new DOMElement('SignatureValue', base64_encode($signedInfoSignature));
+        $SignatureNode->appendChild($SignatureValueNode);
+
+        $KeyInfoNode = $SignatureNode->appendChild(new DOMElement('KeyInfo'));
+
+        $X509DataNode = $KeyInfoNode->appendChild(new DOMElement('X509Data'));
+        $X509CertificateNode = new DOMElement('X509Certificate', $publicCertificatePureString);
+        $X509DataNode->appendChild($X509CertificateNode);
+
+        $X509IssuerSerialNode = $X509DataNode->appendChild(new DOMElement('X509IssuerSerial'));
+
+        $X509IssuerNameNode = new DOMElement('X509IssuerName', $X509IssuerName);
+        $X509IssuerSerialNode->appendChild($X509IssuerNameNode);
+
+        $X509SerialNumberNode = new DOMElement('X509SerialNumber', $X509IssuerSerial);
+        $X509IssuerSerialNode->appendChild($X509SerialNumberNode);
+
+        $envelope = new DOMDocument();
+
+        $envelope->loadXML(
+    '<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
+                <soapenv:Body></soapenv:Body>
+            </soapenv:Envelope>'
+        );
+
+        $envelope->encoding = 'UTF-8';
+        $envelope->version = '1.0';
+        $XMLRequestType = $XMLRequestDOMDoc->documentElement->localName;
+        $XMLRequestTypeNode = $XMLRequestDOMDoc->getElementsByTagName($XMLRequestType)->item(0);
+        $XMLRequestTypeNode = $envelope->importNode($XMLRequestTypeNode, true);
+
+        $envelope->getElementsByTagName('Body')->item(0)->appendChild($XMLRequestTypeNode);
+        return $envelope->saveXML();
+    }
+
+    /**
+     * Sends SOAP request to Croatian fiscalization service.
+     *
+     * @param $payload
+     * @return mixed
+     * @throws Exception
+     */
+    public function sendSoap($payload)
+    {
+        $ch = curl_init();
+
+        $options = [
+            CURLOPT_URL => $this->url,
+            CURLOPT_CONNECTTIMEOUT => 5,
+            CURLOPT_TIMEOUT => 5,
+            CURLOPT_RETURNTRANSFER => true,
+            CURLOPT_POST => true,
+            CURLOPT_POSTFIELDS => $payload,
+            CURLOPT_SSL_VERIFYHOST => 2,
+            CURLOPT_SSL_VERIFYPEER => false
+        ];
+
+        switch ($this->security) {
+            case 'SSL':
+                break;
+            case 'TLS':
+                curl_setopt($ch, CURLOPT_SSLVERSION, 6);
+                break;
+            default:
+                throw new \InvalidArgumentException('Third parameter in CroatianFiscalization constructor must be SSL or TLS!');
+        }
+
+        curl_setopt_array($ch, $options);
+
+        $response = curl_exec($ch);
+        $code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
+
+        curl_close($ch);
+        if ($response) return $this->parseResponse($response, $code);
+        throw new Exception(curl_error($ch));
+    }
+
+    /**
+     * Parses response if an error happens.
+     *
+     * @param $response
+     * @param int $code
+     * @return mixed
+     * @throws Exception
+     */
+    public function parseResponse($response, $code = 4)
+    {
+        if ($code === 200) return $response;
+        $DOMResponse = new DOMDocument();
+        $DOMResponse->loadXML($response);
+
+        $error_code = $DOMResponse->getElementsByTagName('SifraGreske')->item(0);
+        $error_message = $DOMResponse->getElementsByTagName('PorukaGreske')->item(0);
+
+        if ($error_code && $error_message) throw new Exception(sprintf('%s: %s', $error_code->nodeValue, $error_message->nodeValue));
+        throw new Exception(print_r($response, true), $code);
+    }
+}
diff --git a/src/Invoice/Invoice.php b/src/Invoice/Invoice.php
new file mode 100644
index 0000000..f53b327
--- /dev/null
+++ b/src/Invoice/Invoice.php
@@ -0,0 +1,273 @@
+<?php
+
+namespace tonikresic\CroatianFiscalization\Invoice;
+
+use XMLWriter;
+
+class Invoice
+{
+    /**
+     * Invoice UID.
+     *
+     * @var
+     */
+    public int $uid;
+
+    /**
+     * Invoice has tax.
+     *
+     * @var
+     */
+    public $haveTax;
+
+    /**
+     * Date and time.
+     *
+     * @var
+     */
+    public string $dateTime;
+
+    /**
+     * Note of order.
+     *
+     * @var string
+     */
+    public string $noteOfOrder = 'N';
+
+    /**
+     * Invoice number.
+     *
+     * @var
+     */
+    public InvoiceNumber $invoiceNumber;
+
+    /**
+     * Tax rates.
+     *
+     * @var array
+     */
+    public array $listTax;
+
+    /**
+     * Total value.
+     *
+     * @var
+     */
+    public int $totalValue;
+
+    /**
+     * Type of payment.
+     *
+     * @var string
+     */
+    public string $typeOfPayment;
+
+    /**
+     * Operative UID.
+     *
+     * @var string
+     */
+    public string $operativeUID;
+
+    /**
+     * Security code.
+     *
+     * @var string
+     */
+    public string $securityCode;
+
+    /**
+     * Note of redelivery.
+     *
+     * @var bool
+     */
+    public bool $noteOfRedelivery = false;
+
+    /**
+     * Sets UID.
+     *
+     * @param $uid
+     */
+    public function setUID($uid)
+    {
+        $this->uid = $uid;
+    }
+
+    /**
+     * Sets has tax.
+     *
+     * @param $haveTax
+     */
+    public function setHaveTax($haveTax)
+    {
+        $this->haveTax = $haveTax;
+    }
+
+    /**
+     * Sets date and time.
+     *
+     * @param $dateTime
+     */
+    public function setDateTime($dateTime)
+    {
+        $this->dateTime = $dateTime;
+    }
+
+    /**
+     * Sets note of order.
+     *
+     * @param $noteOfOrder
+     */
+    public function setNoteOfOrder($noteOfOrder)
+    {
+        $this->noteOfOrder = $noteOfOrder;
+    }
+
+    /**
+     * Sets invoice number.
+     *
+     * @param $invoiceNumber
+     */
+    public function setInvoiceNumber($invoiceNumber)
+    {
+        $this->invoiceNumber = $invoiceNumber;
+    }
+
+    /**
+     * Sets lists of taxes.
+     *
+     * @param $listTax
+     */
+    public function setListTax($listTax)
+    {
+        $this->listTax = $listTax;
+    }
+
+    /**
+     * Sets total value.
+     *
+     * @param $totalValue
+     */
+    public function setTotalValue($totalValue)
+    {
+        $this->totalValue = $totalValue;
+    }
+
+    /**
+     * Sets type of payment.
+     *
+     * @param $typeOfPayment
+     */
+    public function setTypeOfPayment($typeOfPayment)
+    {
+        $this->typeOfPayment = $typeOfPayment;
+    }
+
+    /**
+     * Sets operative UID.
+     *
+     * @param $operativeUID
+     */
+    public function setOperativeUID($operativeUID)
+    {
+        $this->operativeUID = $operativeUID;
+    }
+
+    /**
+     * Sets security code.
+     *
+     * @param $securityCode
+     */
+    public function setSecurityCode($securityCode)
+    {
+        $this->securityCode = $securityCode;
+    }
+
+    /**
+     * Sets note of redelivery.
+     *
+     * @param $noteOfRedelivery
+     */
+    public function setNoteOfRedelivery($noteOfRedelivery)
+    {
+        $this->noteOfRedelivery = $noteOfRedelivery;
+    }
+
+    /**
+     * Generates security code based on given parameters.
+     *
+     * @param $pkey
+     * @param $uid
+     * @param $dt
+     * @param $bor
+     * @param $opp
+     * @param $onu
+     * @param $uir
+     * @return string [type]       md5 hash
+     * @throws \Exception
+     */
+    public function formatSecurityCode($pkey, $uid, $dt, $bor, $opp, $onu, $uir)
+    {
+        $formattedSecurityCode = '';
+        $formattedSecurityCode .= $uid;
+        $formattedSecurityCode .= $dt;
+        $formattedSecurityCode .= $opp;
+        $formattedSecurityCode .= $bor;
+        $formattedSecurityCode .= $onu;
+        $formattedSecurityCode .= $uir;
+
+        $securityCodeSignature = null;
+        if (!openssl_sign($formattedSecurityCode, $securityCodeSignature, $pkey, OPENSSL_ALGO_SHA1)) {
+            throw new \Exception('Error creating security code.');
+        }
+
+        $this->securityCode = md5($securityCodeSignature);
+
+        return $this->securityCode = md5($securityCodeSignature);
+    }
+
+    /**
+     * Writes to XML.
+     *
+     * @return string
+     */
+    public function toXML(): string {
+        $ns = 'tns';
+
+        $writer = new XMLWriter();
+        $writer->openMemory();
+
+        $writer->setIndent(true);
+        $writer->setIndentString("    ");
+        $writer->startElementNs($ns, 'Racun', null);
+        $writer->writeElementNs($ns, 'Oib', null, $this->uid);
+        $writer->writeElementNs($ns, 'USustPdv', null, $this->haveTax ? "true" : "false");
+        $writer->writeElementNs($ns, 'DatVrijeme', null, $this->dateTime);
+        $writer->writeElementNs($ns, 'OznSlijed', null, $this->noteOfOrder);
+
+        $writer->writeRaw($this->invoiceNumber->toXML());
+
+        // Basic Tax (PDV)
+        if (!empty($this->listTax)) {
+            $writer->startElementNs($ns, 'Pdv', null);
+            foreach ($this->listTax as $tax) {
+                $writer->writeRaw($tax->toXML());
+            }
+            $writer->endElement();
+        }
+
+        $writer->writeElementNs($ns, 'IznosOslobPdv', null, number_format(null, 2, '.', ''));
+        $writer->writeElementNs($ns, 'IznosMarza', null, number_format(null, 2, '.', ''));
+        $writer->writeElementNs($ns, 'IznosNePodlOpor', null, number_format(null, 2, '.', ''));
+
+        $writer->writeElementNs($ns, 'IznosUkupno', null, number_format($this->totalValue, 2, '.', ''));
+        $writer->writeElementNs($ns, 'NacinPlac', null, $this->typeOfPayment);
+        $writer->writeElementNs($ns, 'OibOper', null, $this->operativeUID);
+        $writer->writeElementNs($ns, 'ZastKod', null, $this->securityCode);
+        $writer->writeElementNs($ns, 'NakDost', null, $this->noteOfRedelivery ? "true" : "false");
+
+        $writer->endElement();
+
+        return $writer->outputMemory();
+    }
+}
diff --git a/src/Invoice/InvoiceNumber.php b/src/Invoice/InvoiceNumber.php
new file mode 100644
index 0000000..357dedf
--- /dev/null
+++ b/src/Invoice/InvoiceNumber.php
@@ -0,0 +1,65 @@
+<?php
+
+namespace tonikresic\CroatianFiscalization\Invoice;
+
+use XMLWriter;
+
+class InvoiceNumber
+{
+    /**
+     * Invoice number.
+     *
+     * @var string
+     */
+    public string $numberNoteInvoice;
+
+    /**
+     * Invoice business place label.
+     *
+     * @var string
+     */
+    public string $noteOfBusinessArea;
+
+    /**
+     * Invoice cash register label.
+     *
+     * @var string
+     */
+    public string $noteOfExchangeDevice;
+
+    /**
+     * InvoiceNumber constructor.
+     *
+     * @param $numberNoteInvoice
+     * @param $noteOfBusinessArea
+     * @param $noteOfExchangeDevice
+     */
+    public function __construct($numberNoteInvoice, $noteOfBusinessArea, $noteOfExchangeDevice)
+    {
+        $this->numberNoteInvoice = $numberNoteInvoice;
+        $this->noteOfBusinessArea = $noteOfBusinessArea;
+        $this->noteOfExchangeDevice = $noteOfExchangeDevice;
+    }
+
+    /**
+     * Writes to XML.
+     *
+     * @return string
+     */
+    public function toXML(): string {
+        $ns = 'tns';
+
+        $writer = new XMLWriter();
+        $writer->openMemory();
+
+        $writer->setIndent(true);
+        $writer->setIndentString('    ');
+        $writer->startElementNs($ns, 'BrRac', null);
+        $writer->writeElementNs($ns, 'BrOznRac', null, $this->numberNoteInvoice);
+        $writer->writeElementNs($ns, 'OznPosPr', null, $this->noteOfBusinessArea);
+        $writer->writeElementNs($ns, 'OznNapUr', null, $this->noteOfExchangeDevice);
+        $writer->endElement();
+
+        return $writer->outputMemory();
+    }
+}
\ No newline at end of file
diff --git a/src/Invoice/InvoiceRequest.php b/src/Invoice/InvoiceRequest.php
new file mode 100644
index 0000000..7407b1f
--- /dev/null
+++ b/src/Invoice/InvoiceRequest.php
@@ -0,0 +1,69 @@
+<?php
+
+namespace tonikresic\CroatianFiscalization\Invoice;
+
+use XMLWriter;
+
+class InvoiceRequest
+{
+    /**
+     * Request name.
+     *
+     * @var string
+     */
+    protected string $requestName;
+
+    /**
+     * Invoice.
+     *
+     * @var Invoice
+     */
+    protected Invoice $invoice;
+
+    public function __construct(Invoice $invoice)
+    {
+        $this->invoice = $invoice;
+        $this->requestName = 'RacunZahtjev';
+    }
+
+    /**
+     * Generates UUID.
+     *
+     * @return string
+     */
+    public function generateUUID(): string {
+        return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
+            mt_rand(0, 0xffff), mt_rand(0, 0xffff),
+            mt_rand(0, 0xffff),
+            mt_rand(0, 0x0fff) | 0x4000,
+            mt_rand(0, 0x3fff) | 0x8000,
+            mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
+        );
+    }
+
+    /**
+     * Writes to XML.
+     *
+     * @return string
+     */
+    public function toXML(): string {
+        $ns = 'tns';
+
+        $writer = new XMLWriter();
+        $writer->openMemory();
+
+        $writer->setIndent(true);
+        $writer->setIndentString("    ");
+        $writer->startElementNs($ns, $this->requestName, 'http://www.apis-it.hr/fin/2012/types/f73');
+        $writer->writeAttribute('Id', uniqid());
+        $writer->startElementNs($ns, 'Zaglavlje', null);
+        $writer->writeElementNs($ns, 'IdPoruke', null, $this->generateUUID());
+        $writer->writeElementNs($ns, 'DatumVrijeme', null, date('d.m.Y\TH:i:s'));
+        $writer->endElement();
+
+        $writer->writeRaw($this->invoice->toXML());
+        $writer->endElement();
+
+        return $writer->outputMemory();
+    }
+}
\ No newline at end of file
diff --git a/src/Invoice/TaxRate.php b/src/Invoice/TaxRate.php
new file mode 100644
index 0000000..cf57b87
--- /dev/null
+++ b/src/Invoice/TaxRate.php
@@ -0,0 +1,74 @@
+<?php
+
+namespace tonikresic\CroatianFiscalization\Invoice;
+
+use XMLWriter;
+
+class TaxRate
+{
+    /**
+     * Tax name.
+     *
+     * @var string|null
+     */
+    public ?string $name;
+
+    /**
+     * Tax rate.
+     *
+     * @var string
+     */
+    private string $rate;
+
+    /**
+     * Base value.
+     *
+     * @var string
+     */
+    public string $baseValue;
+
+    /**
+     * Value.
+     *
+     * @var string
+     */
+    public string $value;
+
+    /**
+     * TaxRate constructor.
+     *
+     * @param $rate
+     * @param $baseValue
+     * @param $value
+     * @param $name
+     */
+    public function __construct($rate, $baseValue, $value, $name)
+    {
+        $this->name = $name;
+        $this->rate = number_format($rate, 2, '.', '');
+        $this->baseValue = number_format($baseValue, 2, '.', '');
+        $this->value = number_format($value, 2, '.', '');
+    }
+
+    /**
+     * Writes to XML.
+     *
+     * @return string
+     */
+    public function toXML(): string {
+        $ns = 'tns';
+
+        $writer = new XMLWriter();
+        $writer->openMemory();
+        $writer->setIndent(true);
+        $writer->setIndentString("    ");
+        $writer->startElementNs($ns, 'Porez', null);
+        if ($this->name) $writer->writeElementNs($ns, 'Naziv', null, $this->name);
+        $writer->writeElementNs($ns, 'Stopa', null, $this->rate);
+        $writer->writeElementNs($ns, 'Osnovica', null, $this->baseValue);
+        $writer->writeElementNs($ns, 'Iznos', null, $this->value);
+        $writer->endElement();
+
+        return $writer->outputMemory();
+    }
+}
\ No newline at end of file
diff --git a/tests/CroatianFiscalizationTest.php b/tests/CroatianFiscalizationTest.php
index 3368dc9..cad7c9f 100644
--- a/tests/CroatianFiscalizationTest.php
+++ b/tests/CroatianFiscalizationTest.php
@@ -3,15 +3,101 @@
 require_once __DIR__ . '/../vendor/autoload.php';
 
 use PHPUnit\Framework\TestCase;
+use tonikresic\CroatianFiscalization\Company\Certificate;
+use tonikresic\CroatianFiscalization\Company\Company;
+use tonikresic\CroatianFiscalization\CroatianFiscalization;
 
 class CroatianFiscalizationTest extends TestCase
 {
+    /**
+     * Test certificate path.
+     *
+     * @var string
+     */
+    public static string $certificatePath = 'CERTIFICATE_PATH';
+
+    /**
+     * Test certificate password.
+     *
+     * @var string
+     */
+    public static string $certificatePassword = 'CERTIFICATE_PASSWORD';
+
+    /**
+     * Company UID.
+     *
+     * @var string
+     */
+    public static string $companyUID = 'COMPANY_UID';
+
+    /**
+     * User UID.
+     *
+     * @var string
+     */
+    public static string $userUID = 'USER_UID';
+
     /**
      * Asserts that the fiscalization runs properly.
      *
+     * @throws Exception
      */
     public function testFiscalization()
     {
-        $this->assertEquals(true, true);
+        // Required. Add certificate path and password
+        $certificate = new Certificate(self::$certificatePath, self::$certificatePassword);
+
+        // Required. Add company UID
+        $company = new Company(self::$companyUID, $certificate, true, true);
+
+        // Required. Add user UID
+        $userUID = self::$userUID;
+
+        // Set fiscal abbreviation. G is for cash, K is for credit card.
+        $fiscalAbbreviation = 'G';
+
+        // Invoice gross
+        $gross = 12.5;
+
+        // Invoice net
+        $net = 10;
+
+        // Invoice number
+        $number = 1;
+
+        // Invoice business place label
+        $businessPlaceLabel = 1;
+
+        // Invoice cash register label
+        $cashRegisterLabel = 1;
+
+        // Set Croatian fiscalization data to null
+        $fiscalData = [
+            'zki' => NULL,
+            'jir' => NULL
+        ];
+
+        $invoiceObject = (object) [
+            'userUID' => $userUID,
+            'fiscal_abbreviation' => $fiscalAbbreviation,
+            'company' => $company,
+            'gross' => $gross,
+            'net' => $net,
+            'number' => $number,
+            'business_place_label' => $businessPlaceLabel,
+            'cash_register_label' => $cashRegisterLabel,
+            'fiscal_data' => (object) $fiscalData,
+            'created_at' =>  date('Y-m-d H:i:s'),
+            'fiscal_at' => NULL,
+        ];
+
+        $cf = new CroatianFiscalization();
+        $cf->configure($company);
+
+        $response = $cf->fiscalize($invoiceObject);
+
+        fwrite(STDERR, print_r($response, TRUE));
+
+        $this->assertEquals(true, $response->success);
     }
 }
\ No newline at end of file