Thanks for your help.

In Selling Manager, I went to Awaiting Payment, selected Uncombine Invoices. Then I could select Re-Invoice. I lost my message about Immediate Payment being required so typed it in again. Then Presses Combine Purchases and the invoice was sent again.

Just another quirky thing about EBay. If the buyer uses a phone I  hope the app shows this and he pays. The next communication will be NPB at 4 days.

Why do I have this strict rule. Because If you buy, you pay.