Update services documentation

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

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

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

The issue names services documentation and validation error handling, but no files, tests, or entry points. Start by locating the services documentation and the validation messages it describes; done means the documentation and error messages are more detailed and the relevant checks pass.

Written by the indexing model from the issue text.