Identical duplicate payments are easy to spot. The harder cases change one digit of an invoice number, split one invoice across two remittances, or re-enter a supplier under a slightly different name.
Screen payment history by supplier and approximate amount, not only by exact invoice ID. Many systems treat “INV-1042” and “INV1042” as unrelated. A human review of near-matches still catches what rules miss.
Also watch credit notes applied to the wrong invoice. A credit that reduces balance A while payment still clears balance A’s original amount creates the appearance of overpayment without an obvious duplicate row.
When you find a candidate, reconstruct the timeline: invoice entry, approval, remittance, and bank clearing. That sequence usually reveals whether you have a true duplicate, a timing difference, or a documentation gap that needs a process fix rather than a recovery letter.