Read Albums but can't upload with full access on - Unauthorized

[PeterHuberBJSS]

Hi,

I am trying to create a sync from Google Drive to Google Photos.
Using my Oauth 2 credentials, I can download files from Google Drive.
I can read from Google Photos.
When I try to upload a file I get an issue.

CasCap.Services.GooglePhotosService[0]
StatusCode=Unauthorized, RequestUri=https://photoslibrary.googleapis.com/v1/uploads

Some Issue with header it is says:
{
"code": 16,
"message": "Authentication session is not defined."
}

[f2calv]

Looks like your authentication token hasn't the correct permissions, see https://stackoverflow.com/questions/52092415/authentication-session-is-not-defined