Fix PydanticUserError

✅ Solution

PydanticUserError in FastAPI often arises from incorrect type hinting involving Pydantic models, especially within dependencies or request body definitions. Resolve this by ensuring consistent and explicit type annotations: use `Annotated` correctly for dependencies with `Body()` and verify discriminated unions are properly defined and imported from `typing` instead of `collections`. Consider explicitly defining a Pydantic model schema when using complex types within request bodies.