How I found a duplicate invoice that didn't appear in the standard report

In my day-to-day, I handle accounts payable with recurring vendors and email approvals. The problem that stopped me was this: the monthly expense went up slightly, but there was a duplicate invoice with a different written number. The symptom that made me investigate it seriously was that the vendor was the same, the amount was almost identical, and QuickBooks didn't flag it because it had a new…