Add TypeScript types for types

**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.

Start by locating the API error-handling code and the TypeScript type definitions referenced by the title. Clarify which errors need improved messages and which types are expected before changing anything; done means the intended API errors are descriptive and the requested types are covered.

Written by the indexing model from the issue text.