API Gateway Custom Domain Name | message:not found

I tried to create a HTTP API through API Gateway. This API generated a URL e.g. https://{api-id}.execute-api.{region}.amazonaws.com/ This URL works fine. After this; I created a custom domain name and under "Api Mappings", I added this newly created API., set the stage the $default and left Path (Optional) as blank. This generated another endpoint (which is supposed to be added as an A record in Route53). When I try to hit this new endpoint; I get {"message":"Not Found"}. I followed the documentation as mentioned, but seems to me, that something is missing - any pointers on how to make this work? (Its a minimal configuration and the SSL certificate for the domain is also added)