A payment method that uses a documented purchasing agreement between a buyer and a seller. In large organizations, a procurement department will approve a purchase request and issue a purchase order (P.O.) which can then be referenced when completing transactions that fall under that P.O. Actual payments against a P.O. tend to happen offline from any transactions that would happen on an ecommerce site. When completing an online order via P.O., the buyer will reference the P.O. number instead of providing something like a credit card number. When the order is fulfilled, the merchant’s accounting team will look up the P.O. from the number entered at checkout. If those numbers align, the order is fufilled and the buyer will be invoiced according to the terms agreed upon when the P.O. was first created.