Update services documentation

**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.

No files, tests, or entry points are named. Start by locating the services documentation and middleware error-handling entry points, then clarify which messages require improvement; done means the requested documentation and descriptive errors are updated and verified.

Scritto dal modello di indicizzazione a partire dal testo della issue.