Rob has Quickbooks 2020 and Gmail is blocking his ability to send an invoice. Leo says there's a link in Quickbooks that says "mail this invoice." It will launch Gmail in your browser. If it blocks it, it sounds like Intuit hasn't made a deal with Google to do that. Rob may also have to log into Gmail and authorize it. The authorization can also expire. Check out Google Authorized Apps in permissions at myaccount.google.com/permissions. Delete the old authorization, and the next time Rob sends it, Gmail should pop up with an authorization window for him to reauthorize. Then it should work.