Api gateway throwing {"message": "Internal server error"} after moving to HTTPS.

The error message indicates that there is a certificate mismatch between the certificate subject provided by the peer and the host name 'host.name.ignored.for.vpc.amazon.com'.

To resolve this issue, you need to make sure that the SSL certificate installed on your HTTPS listener matches the domain name used to access your API Gateway.

Here are some steps you can take:

1. Check that the SSL certificate you have installed on the HTTPS listener is valid and matches the domain name used to access your API Gateway. You can do this by examining the certificate's Common Name (CN) field.
2. Make sure that the domain name used to access your API Gateway matches the Common Name (CN) field in the SSL certificate. If they do not match, you will need to update your certificate with the correct domain name.
3. Ensure that the SSL certificate is installed correctly on your HTTPS listener. Double-check the SSL certificate configuration in your API Gateway configuration to ensure that it is set up correctly.
4. If you are using a custom domain name, make sure that the DNS records for your custom domain name are set up correctly to point to the API Gateway endpoint.

If none of these steps help, try reviewing the API Gateway logs for more detailed error messages or contact AWS support for assistance.