How to solve Error: drive.google.com refused to connect?

You open a Google Workspace add-on, such as Formfacade, and in place of its screen you see "drive.google.com refused to connect". It happens when you're signed in to more than one Gmail account in the same browser and the add-on opens with the wrong one. To fix it, use the add-on in an incognito window, signed in with only the account you installed it with.

If you have signed in with multiple gmail accounts in your web browser and try to use any Google Workspace add-on, you might see this error: drive.google.com refused to connect. Please open an incognito window, sign in with your gmail account used to install the add-on (make sure that you haven't signed in with any other gmail account) and try to use the add-on. It should work.

The add-on works when you have signed in with only the gmail account used to install the add-on.

Summary

If you see drive.google.com refused to connect, the add-on is opening with the wrong Gmail account. With an incognito window, signed in with only the gmail account used to install Formfacade, the add-on should work. If you have any questions, write to support.