What should I do if I receive the error "authorization is required to perform that action?"
Cause of the Error
You may receive the error "authorization is required to perform that action" when two or more users with Google accounts share the same web browser, and switch between the two Google accounts.
For example, email@example.com may check his Gmail and then firstname.lastname@example.org may access his Google Drive, thereby switching between two Google accounts. When email@example.com later comes to do a mail merge, he may receive the error above.
This is a documented Google bug.
Load your browser in Incognito/InPrivate mode by pressing Ctrl+Shift+N.
Login to your Google account and run the add-on.
In Google Chrome, create a profile for every person who uses the web browser. Each user can then use their own profile to access their Google account, rather than using a shared profile to do so.
In our example, firstname.lastname@example.org would have his own Chrome profile where he would access all of his Google services. Likewise, email@example.com would have his own Chrome profile where he would access all of his Google services. The error would be avoided as the users would not use multiple Google accounts on the same profile.