tl;dr
Duplicate payments occur when the same invoice is paid more than once, often because it entered the system twice under slightly different references, or because a payment was issued before an earlier one had been recorded as complete.
They're a quiet, recurring source of cash leakage in accounts payable. Automated matching that checks every new invoice against payment history, not just against open invoices, catches the duplicate before it goes out rather than relying on a vendor to notice and refund it.
See how this works in Light's Global bill pay.
