AWS API Gateway 401 "Error: Unauthorized"

I have a simple DynamoDB database that I can access using AWS API Gateway/Lambda functions using POST, GET etc.
I now want to use Auth0 so that only users logged in can access the table. I am able to get an access token from Auth0 and I have followed the instructions here but no matter what I do, I get a 401 error message “Error: Unauthorized”.
I appreciate any help and advice for this issue.

If you haven’t done so already I would suggest starting by testing your version of the custom authorizer locally; see This would allow to troubleshoot any major issues in the authorizer itself so either it fails and you localized the source of the issue or it passes and you at least have an hint that the issue may lie in the remaining configuration in AWS to tie the authorizer to the API calls.