Refactor controllers for better readability

**Problem**
When working with api, 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 controllers and their current error-handling paths; the issue does not name files or tests. Review how existing API errors are produced, then define and verify more descriptive messages for the affected cases, with debugging and maintenance as the stated outcome.

Written by the indexing model from the issue text.