Can't locate actual reference

**Describe the content issue**:

I'm going in circles trying to find an actual reference for the symbols/types in the API docs. For example, where can I see the type returned from `post()`, along with all properties and methods, with descriptions, of that type? What kind of errors are thrown by `post()` and what cause them?

**URL page where content issue is**:

https://docs.amplify.aws/javascript/build-a-backend/add-aws-services/rest-api/post-data/

Start with the REST API post-data documentation page linked in the issue and trace the `post()` API reference from there. Determine where the returned type, its properties and methods, and possible errors are documented; done means the page provides a discoverable reference covering those requested details.

Written by the indexing model from the issue text.