Hi Andrew,

I've read the thread and understand the importance of sending invoices to customers on time. I also recognize the challenges you’ve encountered when doing so. I'll share some workarounds you might consider to continue delivering them.

The investigation mentioned in this thread about undeliverable invoices was resolved. If you are having a similar issue, we can look into that. Can you share more information about your issues? Are you still unable to send invoices? Please know that any additional information can help us provide appropriate solutions.

Aside from downloading invoices and sending them manually, you also have the option to email them through HTML and Plain text. To proceed, follow the steps below:

1. Go to the Gear icon and select Account and Settings.
2. Click the Sales tab then scroll down to Online delivery.
3. Under the Additional email options for invoices, choose which one you'd like to try.

If you're  interested in how their appearance differs from each other, I've got these snippets for you:

For more information about personalising invoices, refer to this article: Customise invoices, estimates, and sales receipts in QuickBooks Online.

I've added this link that will guide you through receiving customer payments: Record invoice payments in QuickBooks Online.

Don’t hold back to drop a comment below if you have any other questions or concerns regarding invoices. I've got your back. Keep safe.