Hi there, andrea55.

I'll work with you in resolving this issue.

We haven't received reports about the undelivered invoices error. Sometimes, this behavior can be caused by a browser hang-up. Let's do some troubleshooting steps to rule this out.

Open an incognito or private browser. This mode doesn't save your browsing history, cookies, site data, or information entered in forms.

Here are the keyboard shortcuts:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Option + P

Then, sign in to your QuickBooks Online account and try to send the invoices. If it's successful, go back to your regular browser and clear its cache. Restart your browser afterwards. Alternatively, try using a different supported browser.

Please let me know in the comments below how it goes after trying out the steps. I'm here to help you out again. Stay safe.