Input, Output and Who Decides
Gather permitted invoices, order or contract lines, acceptance records, payment evidence and correction documents. Produce a five-part evidence table and routed question. The authorized payment owner decides holds, release or recovery; this investigation makes none of those decisions.
Steps
- Put both invoices side by side, retaining their original locators.
- Find the obligation: which order, contract line or agreed milestone could each bill?
- Compare invoice identity, number, date, description and milestone or period. Equal amounts alone are insufficient.
- Find the acceptance or receipt evidence for each obligation under its actual terms.
- Trace payments to the specific invoice and obligation; distinguish execution and allocation from instructions or claims.
- Trace any credit or replacement chain. Before asking about provenance, establish a preexisting independent contact route's integrity and currentness. A stored contact is not automatically trustworthy. Stop and escalate unresolved provenance; callback evidence does not itself authorize payment.
- Compare billed, verified credits, obligation and matched paid totals, retaining unverified amounts separately.
- Route the evidence and unresolved hold or recovery question to the authorized owner.
These are OpenAid's investigation steps, not an automated duplicate verdict.
Two Fictional Cases
All amounts are invented USD.
| Five-part test | A: PO88 | B: PO91 |
|---|---|---|
| Obligation | One accepted 4,500 obligation | Three 2,000 milestones |
| Invoice identity | INV-4410, October 9; INV-4410-R, October 16; both 4,500 | INV-4419/4420/4421 show different milestone labels/periods |
| Acceptance | Supplied for the one obligation | Not supplied for each milestone |
| Prior payment | PAY552 matches 4,500 to INV-4410, October 20 | Payment evidence UNKNOWN |
| Correction chain | CN77, -4,500, references INV-4410, but forwarded email only | Correction evidence UNKNOWN |
Case A has billed documents totaling 9,000. If CN77 is verified, the net billed amount is 9,000 - 4,500 = 4,500, matching the obligation and matched payment. The arithmetic leaves zero additional amount; it is not payment clearance. Without verified CN77, retain the unresolved 4,500 billed excess and its document question. Do not record an unverified credit or pay again simply because a reminder arrived.
Case B's three invoices total 6,000. They may legitimately represent distinct milestones if the actual contract, acceptance, payment and correction chain support that reading. Different labels do not prove acceptance or an unpaid balance. Obtain the missing evidence before classifying them; do not flag all equal-value installments as duplicates.
Exception: Forwarded Credit Note
Retain CN77's provenance gap explicitly. Ask for the original correction chain through an independently assessed suitable route. Do not treat a forwarded file, familiar name or successful callback as proof of every document's authorship or the person's financial authority.
Human Boundary
Report a possible duplicate and evidence gaps, not fraud. Actual delegated owners decide any hold, correction, release or recovery. Trace an outstanding balance when the question is how one obligation's records fit together.
Sources and Scope
The Australian Fraud Prevention Centre's undated duplicate guidance and NHS Scotland's April 29, 2021 guide identify control risks. HMRC's July 27, 2026 procure-to-pay controls and undated VAT-records page support invoice/correction links within UK VAT scope. CC8 (November 27, 2024, England and Wales), ACNC's undated Australian controls and World Bank Contract Management (September 2018, supporting-payment records) inform separate checks and contract evidence. This editorial test imports no tax treatment, advance-payment prohibition or universal authority. Checked November 1, 2026.