Allow a customer to pay any amount he wishes (Overpayment on Invoice)
Allow a customer to pay any amount they have on their balance, above the invoice total.
Would like the ability to tip for petsitting services
D Wilson commented
John on regularly provides additional services that don't show on the invoice, I would like to be able to pay him for his excellent customer service.
Dru Hershey commented
Allow us to pay additional on top of invoice amount.
would like the ability to pay further ahead/more then current amount due