Most invoice disputes in accounts payable trace back to the same underlying problem: the invoice says one thing, but the purchase order or delivery record says something else. The supplier invoiced for ten units; you received eight. The agreed price on the PO was CHF 120 per unit; the invoice shows CHF 135. These mismatches are not always intentional errors — they happen because of partial deliveries, price list updates applied at the wrong time, or a supplier simply not tracking the PO reference.
Three-way matching is the process of comparing the invoice against two other documents — the purchase order and the goods receipt — before approving payment. It is the most reliable way to catch these discrepancies automatically, before money leaves your account.
The three documents and what they cover
The purchase order. Raised by your company before the goods or services are delivered. It records what was ordered, at what price, in what quantity, from which supplier, and under what terms. A well-structured PO is the anchor for everything that follows.
The goods receipt. Created by your warehouse or receiving team when the delivery arrives. It records what was actually received — which items, how many, in what condition. For services, an equivalent confirmation record (signed delivery note or project completion confirmation) plays the same role.
The invoice. Sent by the supplier, requesting payment for what they say they delivered. This is the document your AP team needs to validate.
Three-way matching compares all three. The core checks are:
- Does the invoice reference a valid PO number?
- Does the invoiced quantity match the received quantity (or an acceptable partial amount)?
- Does the invoiced unit price match the PO price?
- Does the line-item description correspond to what was ordered?
When all three documents agree within acceptable tolerances, the invoice can be approved and queued for payment without any manual review. When they do not, the system flags it as an exception and routes it for investigation.
Why it matters more than most AP controls
Two-way matching — comparing the invoice to the PO only — is common but leaves a significant gap. A supplier could invoice for the full PO quantity before delivering anything. Without a goods receipt in the comparison, two-way matching would not catch it. Adding the goods receipt closes that gap.
The impact on dispute volumes is significant. Most invoice disputes fall into a small number of categories: quantity mismatches, price discrepancies, invoicing for undelivered goods, and duplicate invoices. Three-way matching catches the first three automatically. Duplicate invoice detection is usually a separate check, but it is often bundled into the same validation layer in modern AP systems.
For companies dealing with hundreds or thousands of invoices per month, the reduction in manual exception handling is measurable. AP automation programmes consistently show that exception rates drop by 40–60% when three-way matching is properly implemented — not because the matching is new, but because it is now applied consistently, every time, rather than being dependent on individual AP staff catching discrepancies by eye.
The data quality requirement
Three-way matching only works when the underlying data is consistent. This is where many implementations run into trouble.
If your supplier sends an invoice referencing a different PO number format than your ERP uses internally, the system cannot find the match. If unit-of-measure codes are inconsistent — one system counts in pieces, another in boxes — the quantity comparison fails. If the goods receipt is not created promptly, invoices arrive before the receipt exists and sit in a holding queue.
The practical implication is that master data quality is a prerequisite, not an afterthought. Supplier IDs need to be consistent between your procurement and finance systems. Product codes or service categories need to match. PO references need to be communicated to suppliers clearly and they need to include them on their invoices.
Structured e-invoicing helps here. When a supplier sends a PEPPOL invoice or an eBill, the PO reference is a defined field in the document structure — not a free-text note that may or may not be placed consistently. Your ERP can extract it reliably and look up the matching PO without human intervention.
Tolerance thresholds
Exact matching is rarely realistic in practice. Delivery quantities can vary by small amounts due to packaging constraints. Prices can differ by a few cents due to rounding rules applied differently by different billing systems. Three-way matching implementations typically allow for configurable tolerance thresholds — an invoice that is within 1% of the PO price and within an acceptable quantity range passes automatically; one that is outside those tolerances triggers an exception.
Setting those thresholds requires a deliberate decision. Set them too tight and you generate unnecessary exceptions for trivial rounding differences. Set them too loose and material discrepancies pass through unchallenged. Most companies settle on a percentage tolerance for price (often 1–2%) and a separate absolute tolerance for quantity, calibrated to their typical invoice profile.
What happens with exceptions
An invoice that fails three-way matching should not sit in a general AP inbox waiting for someone to notice it. A well-designed approval workflow routes exceptions to the right person immediately: a price discrepancy goes to the buyer who raised the PO; a quantity mismatch goes to the warehouse team who signed off the delivery.
Each exception should carry enough context for the reviewer to make a decision without hunting for documents — the PO line, the receipt record, and the invoice line side by side. How quickly exceptions are resolved has a direct effect on your payment cycle time and your supplier relationships. Suppliers who are paid late because their invoices sit unresolved in an exception queue tend to become less cooperative about other things too.
Three-way matching and structured e-invoicing
The connection between three-way matching and e-invoicing is direct. The more information an invoice carries in a structured, machine-readable format, the more of the matching process can be automated. A PDF invoice requires someone to extract the PO reference, unit price, and quantity manually or via OCR before the comparison can even begin. A structured e-invoice delivers those fields directly into your ERP.
For high-volume AP teams, this is one of the clearest ROI arguments for moving suppliers to structured formats. The matching itself is not expensive — it is the data extraction step that consumes time and introduces errors. Remove that step, and three-way matching becomes close to frictionless for the invoices that match cleanly.