diff --git a/auth0/authentication/async_token_verifier.py b/auth0/authentication/async_token_verifier.py
index b6d5fcee..058e493f 100644
--- a/auth0/authentication/async_token_verifier.py
+++ b/auth0/authentication/async_token_verifier.py
@@ -40,7 +40,7 @@ async def _fetch_key(self, key_id=None):
         key_id (str): The key's key id."""
         return await self._fetcher.get_key(key_id)
 
-    async def verify_signature(self, token):
+    async def verify_signature(self, token) -> dict[str, Any]:
         """Verifies the signature of the given JSON web token.
 
         Args:
diff --git a/auth0/authentication/client_authentication.py b/auth0/authentication/client_authentication.py
index 2b6b345f..849058f4 100644
--- a/auth0/authentication/client_authentication.py
+++ b/auth0/authentication/client_authentication.py
@@ -10,7 +10,7 @@
 def create_client_assertion_jwt(
     domain: str,
     client_id: str,
-    client_assertion_signing_key: str | None,
+    client_assertion_signing_key: str,
     client_assertion_signing_alg: str | None,
 ) -> str:
     """Creates a JWT for the client_assertion field.
@@ -18,7 +18,7 @@ def create_client_assertion_jwt(
     Args:
         domain (str): The domain of your Auth0 tenant
         client_id (str): Your application's client ID
-        client_assertion_signing_key (str, optional): Private key used to sign the client assertion JWT
+        client_assertion_signing_key (str): Private key used to sign the client assertion JWT
         client_assertion_signing_alg (str, optional): Algorithm used to sign the client assertion JWT (defaults to 'RS256')
 
     Returns:
diff --git a/auth0/authentication/token_verifier.py b/auth0/authentication/token_verifier.py
index a08ae5d9..6f745e7c 100644
--- a/auth0/authentication/token_verifier.py
+++ b/auth0/authentication/token_verifier.py
@@ -39,7 +39,7 @@ def __init__(self, algorithm: str) -> None:
             raise ValueError("algorithm must be specified.")
         self._algorithm = algorithm
 
-    def _fetch_key(self, key_id: str | None = None) -> str | RSAPublicKey:
+    def _fetch_key(self, key_id: str) -> str | RSAPublicKey:
         """Obtains the key associated to the given key id.
         Must be implemented by subclasses.
 
@@ -111,6 +111,8 @@ def verify_signature(self, token: str) -> dict[str, Any]:
             or the token's signature doesn't match the calculated one.
         """
         kid = self._get_kid(token)
+        if kid is None:
+            kid = ""
         secret_or_certificate = self._fetch_key(key_id=kid)
 
         return self._decode_jwt(token, secret_or_certificate)  # type: ignore[arg-type]
@@ -128,7 +130,7 @@ def __init__(self, shared_secret: str, algorithm: str = "HS256") -> None:
         super().__init__(algorithm)
         self._shared_secret = shared_secret
 
-    def _fetch_key(self, key_id: str | None = None) -> str:
+    def _fetch_key(self, key_id: str = "") -> str:
         return self._shared_secret
 
 
@@ -144,7 +146,7 @@ def __init__(self, jwks_url: str, algorithm: str = "RS256") -> None:
         super().__init__(algorithm)
         self._fetcher = JwksFetcher(jwks_url)
 
-    def _fetch_key(self, key_id: str | None = None) -> RSAPublicKey:
+    def _fetch_key(self, key_id: str) -> RSAPublicKey:
         return self._fetcher.get_key(key_id)
 
 
diff --git a/auth0/rest.py b/auth0/rest.py
index e1837669..41282b74 100644
--- a/auth0/rest.py
+++ b/auth0/rest.py
@@ -255,7 +255,7 @@ def _calculate_wait(self, attempt: int) -> int:
         wait = max(self.MIN_REQUEST_RETRY_DELAY(), wait)
 
         self._metrics["retries"] = attempt
-        self._metrics["backoff"].append(wait)
+        self._metrics["backoff"].append(wait)  # type: ignore[attr-defined]
 
         return wait
 
diff --git a/auth0/rest_async.py b/auth0/rest_async.py
index 53b92840..183cfbb9 100644
--- a/auth0/rest_async.py
+++ b/auth0/rest_async.py
@@ -1,4 +1,3 @@
-# mypy: disable-error-code=override
 from __future__ import annotations
 
 import asyncio
@@ -115,8 +114,8 @@ async def post(
     async def file_post(
         self,
         url: str,
-        data: dict[str, Any] | None = None,
-        files: dict[str, Any] | None = None,
+        data: dict[str, Any],
+        files: dict[str, Any],
     ) -> Any:
         headers = self.base_headers.copy()
         headers.pop("Content-Type", None)
diff --git a/mypy.ini b/mypy.ini
index f8bc1715..af08759b 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -6,3 +6,9 @@ ignore_errors = True
 
 [mypy-auth0.management.*]
 ignore_errors = True
+
+[mypy-auth0.rest_async]
+disable_error_code=override
+
+[mypy-auth0.authentication.async_token_verifier]
+disable_error_code=override, misc, attr-defined