Thanks for joining in this thread, Bustnastitch.

I understand the time you've spent checking the delivery errors on an invoice in QuickBooks Online. As mentioned by Rasa-LilaM, there isn't a way of notifying the sender about undelivered transactions in QBO. We've lodged customer feedback of the behavior you've encountered about undelivered invoice errors in our customer feedback report to let our Product Development team know.

In the meantime, please continue to check the invoice through your Audit Logs or by opening the actual invoice itself and can check the Last delivery time stamp from there.

If the issue persists, we'd recommend contacting the Customer Care Team so they can further investigate the behavior encountered.

Please leave a comment below if you have other questions in QuickBooks Online. I'll be right here to assist you.