Improve error messages in controllers

**Problem**
When working with handlers, 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 handlers that produce the current errors, then read how those errors are handled. Done means the error messages are more descriptive and the affected error paths have been verified, but the issue does not name specific files or tests.

Written by the indexing model from the issue text.