Google console

You should be able to enable GoogleSheets API here: https://console.cloud.google.com/apis/library/sheets.googleapis.com

There are guides in the internet on how to configure it. However I'll leave the issue open, so at some point a proper guide can be written.

I've added documentation here: https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... →
Hope it helps :)

Automatically closed - issue fixed for 2 weeks with no activity.

Just getting back to this - thanks a lot for the docs - very clear and everything is working. I have screenshots for every step - so I could add these to your docs if it helps. Or if you think about 20 screenshots is too many then I could add them to my own Drupal blog.