Good day, @Eric7780.

There are times when too much cache accumulated in a browser can cause unexpected behavior with the program. This can be the reason why you're invoices are bouncing back to this client. 

We can perform some basic troubleshooting steps to isolate and fix the issue. To start with, try opening QuickBooks on a private window. This is the safest place to tell if you're experiencing some browser-related issues.

I've added these shortcut keys to open one:

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

If you're able to successfully send your invoices, you can go back to a regular browser and clear its cache. Alternatively, you can also use a different browser like Google Chrome, Mozilla Firefox, Safari, or Microsoft Edge.

I've also added this reference for more information in managing invoices: Manage invoices in QuickBooks Online.

There you have it. Let me know if you need further help sending your sales transactions. I always got your back!