I admire you for sharing the troubleshooting steps you've done in fixing the issue, @Bonemd.

I'm here to help you work around this issue so you can manage your QuickBooks Desktop with ease.

I recommend running the Verify and Rebuild tool. This checks your company file for any errors and fixes them right away. 

Here's how:

1. Go to the Window menu and select Close All.
2. Click the File menu.
3. Select Utilities.
4. Click Verify Data.

To Rebuild:

1. Go to the File menu.
2. Select Utilities.
3. Click Rebuild Data.

You can also check this link for more detailed steps: Verify and Rebuild Data in QuickBooks Desktop. 

If the issue remains, I suggest performing a clean install. This uninstalls the program on your computer and reinstalls it in a clean slate. 

Once your customer has received and accepted their email invoice, here is an article that will help you account for their payment: Record an invoice payment.

I'm just a few clicks away from you if need more help with your invoice or QBDT. Stay safe!