Add unit tests for api

**Problem**
When working with middleware, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Start by locating the API middleware and any existing unit-test entry points related to error handling. Reproduce the current middleware errors, then add coverage for descriptive messages and confirm the tests pass.

Written by the indexing model from the issue text.