How duplicate invoices slip through

Very few duplicate payments are fraud. Most are the same genuine invoice getting into the system twice by different routes. Each copy looks legitimate on its own, so each gets approved. Here are the usual ways it happens.

1. The same invoice arrives by two channels

A supplier emails the invoice to accounts, uploads it to a portal, and sends a paper copy with the delivery. Someone keys in one copy, someone else keys in another, and both go into the approval queue.

2. The invoice number is written differently

INV-00042, inv 42 and INV/0042 are the same invoice to a person, but not to a system comparing exact text. Reminders and “copy” invoices often reformat the number, and manual entry adds its own variations.

3. The supplier exists twice in your records

“Acme Supplies Ltd” and “ACME Supplies Limited” set up as two suppliers means a duplicate check scoped to one supplier never sees the other copy. Duplicate supplier records are one of the most common root causes.

4. Reminders and statements get processed as invoices

A payment reminder or statement of account that repeats the invoice details can be entered as a new bill, especially at month-end when volume is high.

5. A reissued invoice without a credit note

The supplier corrects an invoice and sends a new one with a new number, but the original is never credited. Both are now valid documents with different numbers, the same amount and often the same date.

Checks that catch them

• Normalise invoice numbers before comparing. Ignore case, spaces, punctuation and leading zeros.
• Match on supplier identity, not just name. A tax ID (VAT number, ABN, NZ GST number, EIN) is far more reliable than free-text names, and UK VAT numbers and ABNs can be checked against the public registers (HMRC, ABN Lookup).
• Look for lookalikes, not just exact number matches. The same supplier, amount and invoice date under a different number deserves a second look.
• Clean the supplier list. Merge duplicate supplier records (Xero can merge contacts) and control who can create new ones.
• Reconcile supplier statements. A regular statement reconciliation finds double payments that got through.

What Xero does about duplicate bills

Xero has a duplicate bill review. It compares the contact, reference and amount of the bills and credit notes in your organisation, and when it finds possible duplicates it shows a notification at the top of the bills tabs. Choose Review to see each set, then keep them all or void or delete the extras. A bill that has already been paid needs its payment removed before it can be voided. Xero doesn't compare bills created from the same repeating bill template with each other.

It's a useful safety net. Three things follow from how it works:

• It looks at bills already in Xero. Run the review before each payment run, so a duplicate is caught before it is paid rather than after.
• It compares the reference you entered. Put the supplier's invoice number in the reference exactly as printed, and nothing else, on every bill, so two copies of one invoice look the same.
• The contact is part of the comparison. A supplier set up twice in your contacts can hide a duplicate, which is one more reason to merge duplicate contacts.

Where every duplicate check stops

Any duplicate check, Xero's or Tenet's, can only compare the documents it sees. These slip past all of them:

• Invoices paid outside the AP process: on a company card, through an expense claim or by direct debit.
• A payment made straight from a statement or reminder, without a bill being entered.
• The same invoice entered in two companies of a group, each with its own Xero organisation.
• A corrected invoice with a new number and a different amount. Neither check can know it replaces the first; ask the supplier for a credit note against the original.

That's why a monthly supplier statement reconciliation still matters: it compares what the supplier thinks you owe with what you have recorded, wherever the invoices came in.

How Tenet handles it

Tenet compares each new invoice with those already on record. Invoice numbers are compared ignoring case, punctuation and leading zeros. The supplier is confirmed by supplier record, tax ID or normalised name, in that order. The same number from a confirmed supplier is blocking. The same number where the supplier can't be confirmed is a warning. So is the same supplier, amount and date under a different number, unless the two invoices are billed against different purchase orders. Either way the invoice is held with the matching record named, and a person decides. Before posting an approved bill, Tenet also looks in Xero for a bill with the same supplier and invoice number. See invoice validation and duplicate checks for the full list.