Custom auth using Lambda function

I am trying to implement a custom Lambda function in my app in order to check users and federate data. The goal is to be able to federate data based on user using my current user management system. I have created my Lambda function and deployed it. My AppSync setup includes Lambda function as auth method (it is setup as secondary method).

When I test my Lambda function using a valid token, it returns "Authorized", which is expected. Also, when trying to create an elemento from AppSync query dashboard triggering a CreateItem function and specifying a valid token, it works and allows me to create an element. All these steps are logged on CloudWatch.

However, when I try to create an element from my frontend it seems that there's something wrong. It always return "Unauthorized" and I am not able to see logs on CloudWatch from the Lambda function. The data I'm using is similar on the test query and on my frontend, however there should be something wrong on the setup.

I'm a bit blocked on this step, since I don't know what could be wrong at all on my project setup.

This is my Lambda function:

const jwt = require("jsonwebtoken");
const crypto = require("crypto");

const jwkToPem = (jwk) => {
  const keyObject = crypto.createPublicKey({
    key: jwk,
    format: "jwk",
  });

  const pem = keyObject.export({
    type: "spki",
    format: "pem",
  });

  return pem;
};

exports.handler = async (event) => {
  // Log the incoming event to see the full request
  console.log("Received event:", JSON.stringify(event, null, 2));

  // Extract the authorization token from the headers (if available) or from the event directly
  const token =
    event.headers?.Authorization?.split(" ")[1] || event.authorizationToken;

  if (!token) {
    console.log("No token provided.");
    return {
      isAuthorized: false,
    };
  }

  console.log("Token received:", token);

  const secret = process.env.CLERK_API_KEY; 

  const fetch = await import("node-fetch").then((module) => module.default);

  // Fetch JWK from Clerk
  const res = await fetch("https://api.clerk.com/v1/jwks", {
    headers: {
      Authorization: `Bearer ${secret}`,
    },
  });

  if (!res.ok) {
    console.log("Failed to fetch JWK:", res.statusText);
    return { isAuthorized: false };
  }

  const data = await res.json();
  console.log("JWK fetched:", JSON.stringify(data, null, 2));

  const pem = jwkToPem(data.keys[0]);
  console.log("PEM generated:", pem);

  let decoded;
  try {
    decoded = jwt.verify(token, pem);
    console.log(
      "Token decoded successfully:",
      JSON.stringify(decoded, null, 2)
    );
  } catch (e) {
    console.log("Token verification failed:", e);
    return { isAuthorized: false };
  }

  console.log("User is authorized:", decoded.sub);

  return {
    isAuthorized: true,
    resolverContext: { owner: decoded.sub },
  };
};

Also, this is the handler I use in order to create an element:

export const handleAddProvider = async (provider, token) => {
  try {
    console.log("Token:", token);
    const response = await API.graphql({
      query: createProvider,
      variables: { input: provider },
      headers: {
        Authorization: `Bearer ${token}`, 
      },
    });
    console.log("Provider added:", response);
    return response;
  } catch (error) {
    console.error("Error adding provider:", error);
    throw error;
  }
};