API gateway Cognito user pool authorizer - 401 unauthorized

I'd like to submit another really dumb reason why this was not working - definitely do everything in addition to everything that the accepted answer mentioned:

I was performing my testing and validation on Postman. I added in the Authorization header and passed in my id_token. However, I never ticked the checkbox to actually include the header in my actual request: Hope this might save someone out there from spending hours debugging every possible configuration on API Gateway and Cognito only to realize I was never sending the header in the first place!

Turned out to be a really idiotic mistake of copying the access_token as well. With the right id_token it worked. Took me 2 days to figure it out!!!