I found a work around for a customer initiated tip payment.  No thanks to intuit

In your quickbooks setup for your invoice email, include a some language appropriate to your business that tips are not expected but can be left, bla, blah, by EDITING THE PAYMENT AMOUNT on the click and pay screen. 

I sent an invoice to myself.  On the payment options that show up on the click and pay page, where you choose which card you want to use, there is a small field called "edit amount" next to the total. I clicked on it, added a few dollars to my invoice.  It paid and all the money went through. Quickbooks online showed an overpayment, which you can account for later in a tip invoice or however you choose.