serverless/serverless

Hi,
I have a graphql API with authorizer configured. This works fine offline but when deployed to AWS, Authorizer is getting triggered but not getting redirected back to Service. I am getting the below response. (In AWS, i have given Admin access too). Please let me know if i am missed anything.

Response - 500

{
    "message": null
}

Serverless.yml

functions:
  authorize:
    handler: handlers/authHandler.authenticate
  graphql:
    handler: handlers/graphqlHandler.handler
    events:
      - http:
          path: graphql
          method: post
          cors: true
          authorizer: authorize

Auth Handler

module.exports.authenticate = (event, context, callback) => {
    context.callbackWaitsForEmptyEventLoop = false;
    const token = event.authorizationToken;

    try {
      // Verify JWT
      const decoded = jwt.verify(token, process.env.JWT_SECRET);
      const user = decoded.user;
      const effect = "Allow";
      const userId = user.username || user.email;
      const authorizerContext = { user: JSON.stringify(user) };

      // Return an IAM policy document for the current endpoint
      const policyDocument = utils.buildIAMPolicy(
        userId,
        effect,
        event.methodArn,
        authorizerContext
      );

      callback(null, policyDocument);
    } catch (e) {
      callback("Unauthorized"); // Return a 401 Unauthorized response
    }
  };