Optimize controllers for large datasets

**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.

No files or tests are named. Start by locating the API controllers and existing error-handling entry points, then identify the error cases that need more detail; done means the API emits descriptive messages and the relevant behavior is covered by tests.

Written by the indexing model from the issue text.