AR zero or negative payment

We are currently working on a project in which a customer has the ability to pay their invoices via credit card. On some occasions, the amount of credits could be the same or exceed the amount of invoices, resulting in a zero dollar payment or a negative payment. In the Lawson EFT world (AR115), Lawson creates a debit memo to offset the amount of the negative payment and then interjects a zero dollar payment into the payment table.

Has anyone had to create a similar situation and if so, how do you get around the zero or negative payment? I will also be posting this in the Process flow forum.