Mail Merge app has not been verified yet by Google
We just purchased a site license for Mail Merge with Attachment Google Sheet Add-on and it worked just fine for a week.
Now this error message appears:
Sign in with Google temporarily disabled for this app
This app has not been verified yet by Google in order to use Google Sign In.
I see you are working with Google to verify other of your G Suite Marketplace apps. You must be working on verifying the mail merge app too, right? Any idea when it will approved?
Fingers crossed it will be approved soon. 🙂