Duplicate Payment and Anomaly Detector for AP Ledgers

Two families of check, kept apart on purpose, because one is arithmetic and the other is judgement.

Duplicate checks

These compare invoices against each other and look for the same money twice.

• The same invoice number, whoever it is under. Deliberately not scoped to one vendor. An invoice number repeating across two vendor records is usually one company entered twice in the vendor list, and it is often the most valuable thing a first scan finds, because grouping by vendor first is exactly what hides it.
• The same vendor, amount and date, under different invoice numbers. One document entered twice, each time picking up its own reference. The vendor is required here: two suppliers billing the same amount on the same day is a coincidence, not a duplicate.
• Invoice numbers that differ only in formatting. NG-00318 and ng318 are the same reference written twice. Punctuation and leading zeros are stripped before comparison.
• The same vendor and amount close together, where the dates follow no regular pattern.
• A credit note matching an invoice that was still paid in full.

Anomaly checks

These do not compare invoices to each other. They compare the ledger to what a ledger usually looks like, and each one produces a question rather than an answer: round-number concentration against your own baseline, a new vendor paid a large amount immediately, a dormant vendor waking up after a year, and invoice numbers from one vendor running nearly consecutively.

Above 500 invoices a first-digit distribution is also reported. It is a comment on a population and says nothing about any individual invoice.

The widest duplicate check looks for the same vendor and the same amount inside a window, and on its own it would fire on every monthly rent payment, every annual renewal and every quarterly retainer in the ledger.

So anything repeating on a regular cadence, three or more times at a consistent interval, is classified as recurring and moved into its own section. It is still reported, because a real duplicate can hide inside a recurring series, and a payment that arrives far sooner than the schedule allows is pulled back out and reported on its own.

This matters more than it sounds. A tool that reported twelve months of rent as twelve duplicates would show you twenty-two findings instead of four, and you would stop reading at about number six.

It is not an audit. It produces candidates. Every one needs a person to open the invoice, check the payment record and decide, and the tool cannot see a credit you have already taken or a recovery you have already made.

It is one check of six. Adopt's AP agents run this same duplicate check and five more on every invoice before it is booked. The other five need your vendor master, your open purchase orders, the currency your books are kept in, and the invoices arriving alongside the one being checked. None of that is in a spreadsheet.

It has no memory. Nothing is stored, which is the same property that keeps it private. Run it twice and it will show you the same things twice, including whatever you have already dealt with.

Accounts payable only, one currency at a time, and no vendor or bank verification of any kind.