API Gateway Authorizer - IAM policy not caching

I am trying to cache the IAM policy returned by the authorizer lambda when it validates the JWT token for the first time. I have enabled and set the authorizerResultTtlInSeconds to 3500 seconds in API Gateway Authorizer. However, I still see a request going to the Authorizer lambda function within the caching time frame as this shouldn't happen due to caching.

My node.js script is as below:

const jwt = require('jsonwebtoken');
const jwksClient = require('jwks-rsa');

const keyClient = jwksClient({
    jwksUri: process.env.JWKS_URI
})

const allow = {
    "principalId": "user",
    "policyDocument": {
        "Version": "2012-10-17",
        "Statement": [
            {
                "Action": "execute-api:Invoke",
                "Effect": "Allow",
                "Resource": process.env.RESOURCE // RESOURCE = *
            }
        ]
    }
}

const unauthorized = {
    "error": "Unauthorized",
}

//excluded verificationJWTOptions object and getSigningKey function for simplicity
function validateJWTToken(token, callback) {
    jwt.verify(token, getSigningKey, verificationJWTOptions, (error) => {
        if (error) {
            callback(unauthorized)
        } else {
            callback(null, allow)
        }
    })
}

exports.handler = (event, context, callback) => {
    const token = extractTokenFromHeader(event);
    validateJWTToken(token, callback);
}

Not sure what I am missing out. Any help would be much appreciated!

No repository file or test is named; the issue provides only an inline Node.js authorizer handler. Start by reviewing the API Gateway Authorizer configuration and the shown exports.handler and validateJWTToken flow, then reproduce requests within the 3500-second TTL. Done means identifying why the authorizer is invoked during the configured caching window and documenting the verified behavior or required configuration.