Can someone please explain to me what a Purchase Order is ? Someone contacted me for a service and they said they "will be paying with Purchase Order". I do not want to sound like an idiot. But as someone who is providing the service, what specific action should I take when someone wants to pay with a Purchase Order ? Do I send an invoice ? We already agreed on the price, and I just wanted them to send me a check or pay online. This "purchase order" thing just threw me off. I do not know what to do next.