Welcome to the Community, @Maura! 🙂
I did some checking and found that we’ve got an existing feature request for the ability to trigger on past due invoices (as well as ones due in X number of days). Which sounds like it’s what you’re looking for here so I’ve added your vote to that.
I can’t make any promises as to when that sort of trigger would be added to the Quickbooks Online app, but we’ll be sure to email you as soon as it becomes available!
In the meantime, do you have a different Zap that creates the invoice and sets the due date?
If so, I’m thinking you could add an action to that Zap to add a calendar event on the day the invoice is due, or X number of days after it. Then you could have a Zap that triggers when that event starts and sends out an email notification. Do you think that approach could work or are the invoices added manually?