Attempting to run a Google Workspace add-on when logged into multiple Google accounts often causes problems.
Unfortunately, Google is unable to determine which account is running the add-on, so if you are logged into more than one account, permission is denied to access your document.
For Please Sign Me, this stops us from inserting variables, or actually accessing the document at all. It may appear like the add-on runs, because the sidebar opens up, but behind the scenes we can't do anything.
You have two main options:
1. Log out of all your Google accounts, except for the one which has access to the document you are using with Please Sign Me.
2. Instead of logging into multiple accounts, use multiple profiles in Chrome. Learn more about Chrome profiles.
We're happy to help get you over the hump on this. Please reach out to us at firstname.lastname@example.org and we'll do what we can.