What documents are matched?
The first document is the purchase order. It records what you agreed to buy, how many and at what price. It is your record of the deal.
The second is the goods received note. Someone checks the delivery in and records what arrived. For services, a sign-off from the person who received the work plays the same role.
The third is the supplier's invoice. Your accounts payable team lines it up against the other two. They check the supplier, the items, the quantity and the price. If all three agree, the invoice moves on for payment.
Two-way vs. three-way vs. four-way match
A two-way match compares only the purchase order and the invoice. It confirms you are billed what you agreed to. It does not confirm you received anything.
A three-way match adds the goods received note. That extra step catches invoices for items that never arrived or arrived short.
A four-way match adds an inspection record. It suits goods that must pass quality tests before you accept them. Pick the level that fits the risk and value of what you buy.
Common mismatch causes
Quantity gaps are a common cause. A supplier may ship part of an order and invoice for all of it. It may also send two invoices for one delivery.
Price gaps are another. The invoice may use an old price list. It may add charges that were not on the purchase order, such as freight or rush fees.
Some mismatches are simple data errors, like a wrong order number or unit of measure. Anything that does not agree goes back to the buyer or the supplier to fix.
How to automate the match
Start with clean purchase orders. Clear item codes, units and prices give the system something exact to compare.
Record deliveries on the day they arrive. The match cannot run until the goods received note exists, so a late receipt holds the invoice.
Then let software do the comparison. Many purchase-to-pay systems match the three documents on their own and flag only the exceptions. Many teams also set a small tolerance so rounding gaps do not stop payment. Your team then spends its time on the invoices that need a person.