Three-Way Matching Explained: PO, GRN, and Invoice

Three-way matching is one of the most important controls in accounts payable. Before you pay a vendor invoice, finance verifies that three documents agree: the purchase order (what you ordered), the goods received note (what arrived), and the vendor invoice (what you are being charged).

When these documents match, you pay with confidence. When they do not, you hold payment until someone investigates.

The three documents

Read our full guide on what is a goods received note (GRN) for receiving workflow details.

How three-way matching works

1. PO issued — procurement creates a purchase order with line items, quantities, and agreed prices
2. Goods received — warehouse completes a GRN noting quantities received vs ordered
3. Invoice arrives — vendor sends an invoice referencing the PO number
4. AP matches — finance compares all three: same vendor, same PO reference, matching quantities and totals
5. Approve or hold — matching invoices go to payment; mismatches go to exception review

Common mismatch scenarios

• Short shipment — PO ordered 100 units, GRN shows 90 received, invoice bills for 100
• Price change — PO price differs from invoice (verbal agreement not updated in system)
• Missing GRN — invoice arrives before receiving team files the receipt
• Wrong PO reference — vendor cites a different PO number on the invoice

Each scenario should trigger a hold, not an automatic payment.

Manual vs automated matching

Manual matching works for low volume: an AP clerk opens three PDFs side by side and compares line by line. At 50+ invoices per month, this breaks down.

Automated matching extracts structured data from each document type:

• Purchase order parser — PO number, vendor, line items
• Packing slip / delivery note parsing — received quantities
• Invoice parser — vendor, totals, PO reference, line items

AutoDocParse compares extracted fields and routes mismatches to the review queue before data posts to your ERP.

Building a three-way match workflow

If you are starting from scratch, follow our invoice processing automation guide and add these steps:

1. Require PO numbers on all non-PO invoices above your threshold
2. Mandate GRN completion before invoice approval
3. Parse all three document types into structured JSON
4. Set tolerance rules (e.g. ±$0.01 on totals, exact match on quantities)
5. Route exceptions to a named reviewer with audit logging

Use our accounts payable automation checklist to track progress.

Free templates to get started

• Purchase order generator — create PO PDFs with SKU line items
• Delivery note / GRN generator — record ordered vs received quantities
• Invoice generator — test what vendor invoices look like on the other side

Next steps

Start with 20 free credits per month on AutoDocParse. Upload sample POs, GRNs, and invoices from your top vendors, then measure match rates before scaling. Pair with Zapier or webhooks to push approved matches to your accounting system.