Stopping a supplier invoice being paid twice
How duplicate supplier invoices creep into a non-profit's books, and the supplier list, invoice-number block and matching that stop a second payment.
By Achekam · · 5 min read · For Non-profit businesses in South Africa, Nigeria, Kenya
A printer supplies the annual report and sends an invoice by e-mail. A copy comes with the delivery. A month later the supplier's statement arrives, and then a reminder with the invoice attached again. Four pieces of paper, one debt. In a busy office with a part-time bookkeeper and a programme manager who forwards everything "just in case", it is easy for two of them to be paid.
Most suppliers will refund a duplicate payment when asked, but not all, and not quickly. Meanwhile a restricted grant has been charged twice for the same cost, the budget comparison is wrong, and if a funder's auditor finds the duplicate before you do, the question becomes whether your controls work at all.
This article explains how duplicates happen and the checks in Achekam that stop them, along with the habits that cover what the system cannot.
How duplicates happen
Nearly every duplicate payment starts with a document that looks like an invoice but is not a new one:
- copies: the same invoice sent by e-mail and on paper, or forwarded by two colleagues;
- reminders: a "second notice" with the invoice attached again;
- statements: a list of open invoices treated as a bill in its own right;
- pro-forma or quotation documents: paid as if they were the final invoice, and then the real invoice paid as well;
- two routes into the books: the same invoice captured once as a bill and once through document upload.
That last route deserves attention. Supplier invoices uploaded to Financial Intake become journal suggestions, not bills on the Bills list to pay. If someone uploads an invoice to intake while someone else enters it as a bill, the same cost can reach the ledger twice. Decide which route each kind of invoice takes, and tell the team.
One supplier list, checked for duplicates
Duplicate suppliers lead to duplicate payments. If "ABC Printers" and "A.B.C. Printers (Pty)" both exist, each can carry the same invoice without anyone noticing.
Achekam keeps one supplier list, with duplicate checks by name or VAT number, and quotations, orders and bills pick suppliers from it. Use that to your advantage:
- Allow only one or two people to add suppliers.
- Before adding one, search the list for similar names.
- Record the VAT number wherever the supplier has one.
- Review the list each quarter and merge or switch off obvious duplicates with your accountant's help.
One limit at the time of writing for Nigerian and Kenyan organisations: a supplier's VAT number must be in the South African format, so Nigerian and Kenyan VAT numbers are refused. The name check still works, but you cannot rely on the VAT number check, so the manual search before adding a supplier matters more.
The supplier's invoice number as a block
When a supplier invoice is recorded against a purchase order and posted, it goes into the ledger as expense, input VAT and trade payables, and the supplier's invoice number stops it being posted twice. A reminder or a second copy carrying the same invoice number cannot be posted a second time, so it does not quietly become a second debt.
The block only works if the number is captured exactly as the supplier printed it. Agree a rule: always the supplier's own invoice number, never your internal reference, and no added spaces, prefixes or abbreviations.
For documents that come in through Financial Intake, journals proposed from documents are only candidates. Only a person can approve and post one, and possible duplicates wait in the Intake Review Queue for a person to decide. Treat every possible-duplicate flag as a stop sign until someone has compared the two documents side by side.
Matching to the order and the delivery
The strongest protection against paying for the wrong thing, or paying twice, is to pay only for what was ordered and received.
In Achekam, a supplier invoice recorded against an order is matched with what was ordered and what arrived. If the price or quantity differs, the invoice is held until someone writes a resolution note explaining the difference. AccountingTools' explanation of three-way matching describes this comparison of the supplier invoice, the purchase order and the receiving record before payment.
Not every cost has an order. Supplier bills can also be recorded line by line with VAT without one, but a bill without a purchase order waits for approval before it posts. Make the approver's job explicit: before approving, check that no bill for the same supplier, amount and date is already recorded or paid. Bills without a purchase order covers that route in more detail.
A check before each payment batch
Bills can be paid in full or in parts from a chosen bank account. Paying in a batch, once or twice a month, makes a final review possible. Before releasing any batch:
- Sort by supplier and amount. Two bills from the same supplier for the same amount are the most common duplicate. Investigate every pair.
- Compare invoice numbers. Look for numbers that differ only by a character or a prefix.
- Check against last month's payments. A bill paid last month should not appear again this month.
- Look for statements and reminders. Anything titled "statement" or "reminder" should not be in the batch at all.
- Separate the duties. The person who prepares the batch should not be the only person who approves it.
Write down who ran the check and what they found, even when the answer is "nothing". That note is evidence for a funder that the control runs.
When a duplicate gets through anyway
If a duplicate is paid, ask the supplier promptly, in writing, for a refund or a credit against the next invoice. Record what you agree and keep the correspondence.
For a wider look at warning signs in buying, see spotting warning signs in purchasing, and for how supplier choices are evidenced for funders, showing funders how a supplier was chosen.
Run the payment-batch check on your last three months of supplier payments this week. If it finds nothing, you have evidence your controls work; if it finds something, you have found it before an auditor did.
General guidance only, not advice on your own circumstances. Tax and payroll rules change: check the current position with the authority or your adviser.
