I appreciate you for bringing this issue to our attention. Let me help you fix this issue, @dprice-xix-gmail.

To start, did you receive an error code when sending an invoice? When using a mobile application, you’ll need to make sure you have the updated version so you won’t receive errors when sending invoices. 

I also recommend logging in to your QuickBooks Online account on a browser. This way, it will help us identify if it is a mobile app issue.  

 If it works on a browser, here are a few troubleshooting steps to get this working on your mobile app.

• Restart your phone and launch again the app.
• Update your phone's operating system.
• Uninstall/Reinstall the app.

Let me know how this goes so we can further assist you. Thanks!