What is a duplicate invoice and how do you handle one?

Duplicate invoices happen most often by accident. A staffer creates an invoice in your accounting software, the system glitches and appears not to save it, the staffer creates it again, and now there are two invoices for the same work. The customer receives both, often pays one and ignores the other, and your AR aging report shows an unpaid invoice that should not exist.

The resolution is to identify which invoice is the genuine one (usually the earlier one if both are otherwise identical), confirm with the customer that they paid against that one, and void or credit-memo the duplicate. Most accounting platforms support a 'void' action that maintains the audit trail without affecting the books. If a credit memo has already been applied or the customer has paid the wrong invoice, the cleanup gets more complex but is still tractable.

Less commonly, duplicate invoices appear in fraud patterns — a vendor or insider intentionally bills the same charge twice hoping the customer pays both without noticing. This is more common in B2B contexts with high-volume invoicing where individual invoices do not get scrutinized. Detection usually requires a periodic audit of the AR aging report against actual work performed, or a customer noticing the duplicate and flagging it. The right response, if duplicate billing is intentional and persistent, is a chargeback dispute or fraud investigation.