Duplicate Payments: Causes and Detection

What are duplicate payments?

A duplicate payment is a payment on a supplier invoice that had already been paid, in full or in part. It is rarely intentional: it almost always comes from a mistake when the invoice is recorded or in the approval flow. The supplier may refund the amount, but getting it back takes time, and sometimes nobody notices.

Duplicate payments are not the same as a duplicate invoice in the legal sense, which is a copy of an issued invoice. Here we mean recording or paying the same invoice more than once.

What causes duplicate payments?

• The supplier sends the invoice again: by email and on paper, or again as a reminder, and it gets recorded twice.
• Typing errors: the invoice number is entered with an extra zero, a hyphen or a space, and the system doesn't recognize it as the same one.
• Supplier set up twice: the same supplier exists as two records, and each copy of the invoice goes to one.
• Split approvals: two people approve the same invoice through different routes.
• Manual payments outside the flow: an urgent payment is made by bank transfer and the invoice then goes through the normal process.
• Integration retries: a dropped connection makes an integration send the same invoice to the ERP again.

Duplicate invoice detection

Detection works better before payment than after. The usual checks are:

1. Compare each new invoice with those already recorded by supplier, number, date and amount.
2. Normalize the invoice number (remove spaces, hyphens and leading zeros) before comparing.
3. Look for near matches, not only exact ones: same amount and supplier with close dates.
4. Review supplier master data to merge duplicate records.
5. Reconcile regularly with the supplier's statement of account, which shows any overpayments received.

Near matches produce false positives, so they usually go to a review queue instead of being blocked outright.

An example

A supplier emails invoice FA-2026-0154. A week later they send it again with the subject "reminder", and someone else records it as FA20260154. The system doesn't see two identical numbers, so both go to payment. A rule that normalizes the number and compares supplier and amount would have flagged the second one as a possible duplicate.

Duplicate payment prevention at DPI

The supplier invoice automation DPI describes includes duplicate prevention within the flow: document extraction, validation against purchase orders and master data, approval and controlled creation of the record in the ERP. It also recommends testing retries and dropped connections before enabling posting, so a network outage doesn't turn into a duplicate entry in the books.