I was trying to setup gdrive backup in v16 but it failed upon authorization and got this error. Used to work fine on V15
Anyone had success connecting Gdrive?
When I click Authorize button it is redirecting to: frappe.integrations.google_oauth.callback
After login to Google account and continue, I am getting above error.
Is the call back url: this?offsite_backups.offsite_backups.doctype.google_drive.google_drive.authorize_access
But, why when clicked authorise takes frappe.integrations.google_oauth.callback??
Help, anyone? 
When I click the Authorize button, it redirects to frappe.integrations.google_oauth.callback, and after logging into my Google account and continuing, I encounter the same error.
Could be this issue Invalid Google Callback on latest Frappe · Issue #14 · frappe/offsite_backups · GitHub
Just check if backup works, then you can ignore the error
Looks like the callback is tripping over something in v16. I got the same loop and what helped me for now was checking if the backup job actually ran in the background even though the OAuth screen threw an error. Also worth peeking at the Google credentials to make sure the redirect URL still matches, since v16 seems picky about that. The GitHub thread folks are already poking at a fix.