Ask HN: Unsolvable 403 errors with Google Photos API?

I've been trying to get a simple app working with the Google Photos Library API, but I'm completely stuck on a persistent 403 PERMISSION_DENIED error with the message "Request had insufficient authentication scopes".

I'm trying to make a simple GET request to https://photoslibrary.googleapis.com/v1/mediaItems.

To be absolutely sure it wasn't a missing scope, I tried requesting every single scope that exists for the Photos Library API (photoslibrary, sharing, appendonly, readonly, etc.). It made no difference; the result was still 403.

Here is everything I've tried to fix it, without success:

- Confirmed the "Photos Library API" is enabled in my Google Cloud project.

- The OAuth Consent Screen is correctly configured in "test mode" with my accounts added as test users.

- I have created brand new OAuth 2.0 credentials.

- I have created a completely new, clean Google Cloud project from scratch.

- I have tried authenticating with multiple, different Google accounts (including a brand new one).

I can reproduce the exact same 403 error using Google's own OAuth 2.0 Playground when configured with my project's credentials.

I've even wondered if it might secretly require some Google Drive scopes, which would be strange and is completely undocumented, but I'm running out of ideas.

Could anyone with a working Google Photos API integration confirm if it's still working for them?