I have a customer whose last invoice was in a previous year and was paid with credits accumulated from years prior to that (they always overpaid a little each month). The invoice is marked paid and all credits have been applied. The customer balance is zero. For some reason the A/R shows the amount of this invoice still years later. How do I clear this up without messing up prior year financials? We are on cash basis but use invoices to keep track of our customers.