Fix issues with multiple Google accounts
Due to bug #69270374 [1] with Apps Script [2], users with multiple Google accounts signed in at once [3] on a browser may experience issues while using the add-on.
To fix issues from multi-login, try one of the following solutions:
Open your browser in private/incognito mode.
Sign out of all your Google accounts and only sign in to the one that has Budget n Sheets authorized.
Notice Bug #69270374 is not exclusive to the add-on Budget n Sheets: it affects all Apps Scripts projects.
References
"Unexpected "authorization is required" error from google.script.run after installing Sheets add-on while logged into multiple gmail.com accounts", Google Issue Tracker
"Fix issues with multiple Google Accounts", Google Apps Script
"Sign in to multiple accounts at once", Google Account Help