Greetings, wpoynter.
Thanks for posting your concern here in the Community. I'm here to provide information about how you can send the invoices successfully.
Undelivered invoices are usually happening if the email address entered is invalid. It's also possible that there was an issue with your recipient's email server.
You can open your invoice again and review if the email entered is correct. If correct, please try to send the invoice to check if the problem persists.
We can also try to use a different email address to determine if the problem is email related. For more information about Undelivered invoices, check out this article:
Undelivered Invoices in QuickBooks Online
If the email address is correct and you're still unable to send email, I recommend you give us a call. We've received reports from other users about not being able to send invoices with the correct information. You can let one of our Phone Support Team check if you're affected to the investigation number INV-20282.
You can reach them through this article: Get help with QuickBooks Online
The Community team has your back whenever you need more help with the invoices. Please don't hesitate to reach out by leaving a comment below.
