Add TypeScript types for config

**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, entry points, or tests are named. First inspect the configuration and API error-handling entry points, and clarify whether the intended work is TypeScript config types, more descriptive errors, or both. Done should mean the agreed config types and error behavior are implemented and covered by the relevant tests.

Written by the indexing model from the issue text.