If all the permissions from the OAuth screen were not selected, you must remove the Datagran app from Google and do the process again. Go to  Apps with access to your account

https://myaccount.google.com/u/1/permissions?pli=1&pageId=none

and click in “Remove access”

https://lh3.googleusercontent.com/vScgFvI7C55aJ5EyDRCNcJAV7nnkPplTSe6GK0CznJ8ZPKnew0KXV81RWwCHBIYPneGpv5fh8vE1zg1mCFEFd_XBdKC6Gs0etPiLsiNrGmZtZSEFkdYMYGv96XV7DSynE6sivNu1

next you can Sign in with Google in Datagran and select all permissions

https://lh6.googleusercontent.com/SMFBROKyvZEVjYv0jOpyoT_ZhCY9x7ZXLjzk1oTMjqQxMuOjmALgoKExSE2EqNKbPryX0fhD_xHRJkvZckG0-4T3fWj3E3Vk8DWhYbu49oaZtvEBIC_6F0HKgzilghSJu32wSUR_