Cannot add Elasticsearch Data Source: Request failed with status code 400

None of the fields are highlighted in red to indicate a problem.

I was able to select the region and ES domain.

I tried selecting an existing role, which i created by following this AWS tutorial: https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-elasticsearch-resolvers.html. That resulted in another strange error: "Error: Only amazonaws.com domains are supported at this point." My ES domain endpoint does contain amazonaws.com...

I opened a support case with AWS support but it's been almost 2 days and nobody has responded yet so I am giving this forum a chance.

Has anyone experienced this problem? Any ideas how to resolve it?

Thank you in advance.