No support for AWS OpenSearch Serverless in HTTP Request nodes?

I am trying to make a POST request to add a document to an OpenSearch Serverless index using a HTTP Request node. I select AWS predefined credential type and add my AWS credentials, including key, secret and region.

In n8n 1.95.3 version there is no way to select “Service”. So my understanding is that for AWS credentials, the node infers the service based on the endpoint URL. Since my endpoint is for OpenSearch https://…com/_bulk, I understand that it may be trying to use the “es” service instead of the serverless “aoss”, and I get a “Forbidden” error.

Is there a way to specify the “aoss” Service in the AWS credentials in an HTTP Request node? Is it defaulting to “es” service and that is why I’m getting the Forbidden error?