An invoice arrives by post; the same invoice arrives two days later by email. A supplier sends a reminder with a new number although the first invoice is already paid. Two people in the company approve the same document. That is how double payments happen. They are rarely noticed straight away, and the money does not come back on its own.
This article explains how to recognise a duplicate supplier invoice, how to organise the check in daily work, and what to do if you have already paid twice.
How double payments happen in a small business
The most common causes are not fraud but process:
- Several channels. The invoice is a PDF in the inbox, a sheet of paper on the desk and a copy attached to the reminder.
- Reminder instead of copy. Some suppliers generate a new document with a new date for the reminder. If you only compare dates, you see two invoices.
- Advance and final invoice. In construction or project work, the advance invoice and the final statement overlap. Without reconciliation, the advance is paid twice.
- Several people pay. If two people have e-banking access and no shared list, each pays what they see.
- Supplier created twice in the accounts, under the old and the new name. The software does not see the duplicate.
What to compare to identify a duplicate
A duplicate invoice is rarely an exact copy, so check several attributes together:
- Supplier's invoice number. Same number, same supplier: almost certainly a duplicate.
- Amount and currency. Same total from the same supplier within a few weeks is a warning sign, even with a different number.
- Invoice date and date of supply. Under Art. 26 of the Swiss VAT Act, an invoice states the date or period of the supply. Same period and same amount points to double billing.
- QR reference. The Swiss QR-bill carries a reference the supplier assigns per receivable. Two documents with the same QR reference belong to the same receivable.
- IBAN and payee. Identical on a genuine duplicate. If the IBAN differs, it is not a duplicate but a different problem (see changed IBAN).
No single attribute is enough. A reminder has a new date but the same reference. An advance invoice has a different number but the same period of supply.
Why the comparison must go back months
Double payments often come with a delay: the reminder arrives 30 to 60 days after the first invoice. If you only compare this week's invoices, the first one is out of sight. The comparison should cover at least the last three to six months, and the whole project for construction suppliers.
You have to keep the documents anyway: under Art. 70 of the VAT Act and Art. 958f of the Code of Obligations, books and vouchers are retained for ten years. The Federal Tax Administration (FTA) can assess a tax claim up to five years after the end of the tax period (Art. 42 para. 1 VAT Act). An invoice booked twice also means input tax deducted twice, and that shows up in an audit.
What to do if you have already paid twice
- Inform the supplier in writing and request a refund, stating both payment dates and amounts.
- Offset against the next invoice, if the supplier agrees. This is often faster than a refund.
- Correct the accounts. The second payment is not an expense but a receivable from the supplier. Input tax may be deducted only once.
- Call the bank if the second payment was made today or yesterday. It can sometimes still be stopped.
You are entitled to the money back, but recovering it takes time, especially if the supplier has since ceased trading.
Checklist: avoiding double payments
- One person approves, or the four-eyes principle applies.
- Every incoming invoice is logged: supplier, number, date, amount, QR reference, status.
- Before each payment: number, amount and reference are checked against the last six months.
- Reminders are never paid directly; the original invoice is located first.
- Advance and final invoices are laid side by side and the deduction verified.
- Paid invoices are visibly marked, including the paper version.
- The supplier master list is cleaned of duplicates regularly.
Matching duplicate invoices automatically
Klyrenta compares each uploaded supplier invoice (PDF or photo) with the last 2,000 invoices in your account and flags duplicates with the reason: same number, same amount, same reference. It also runs the other checks: net plus VAT equals total, VAT rate valid on the date of supply, IBAN unchanged compared with earlier invoices. The result is OK, Warning or Error per invoice, with an Excel export.
Klyrenta pays nothing, books nothing and decides nothing. It shows what to look at before you pay. Data is hosted in Switzerland at Infomaniak; uploaded files are deleted after 90 days.
The first 10 invoices are free, then CHF 49 one-time for 100 invoices or CHF 59 per month for 200. Details: Invoice review for SMEs.
Checked against the official sources named in the text.