2-way, 3-way, 4-way matching

2-way matching verifies that Purchase order and invoice information match within your tolerances:
Quantity billed <= Quantity Ordered
Invoice price <= Purchase order price

3-way matching verifies that the receipt and invoice information match with the quantity tolerances defined:
Quantity billed <= Quantity received

4-way matching verifies that acceptance documents and invoice information match within the quantity tolerances defined:
Quantity billed <= Quantity accepted.
(Acceptance is done at the time of Inspecting goods).

Whether a PO shipment has 2-way, 3-way or 4-way matching can be setup in the Shipment Details tab when entering the PO

RECEIPT REQUIRED(Yes) + INSPECTION REQUIRED (Yes) = 4-Way MATCHING
RECEIPT REQUIRED(Yes) + INSPECTION REQUIRED (No) = 3-Way MATCHING
RECEIPT REQUIRED(No) + INSPECTION REQUIRED (No) = 2-Way MATCHING