We don't sell on Purchase Orders (PO's)!
A Purchase Order is not a payment — it's a stated commitment of future payment and you would have to pay for the license by any of the supported Payment Options as well. Purchase Orders also made sense in the world of manufacturing, where it would take months or maybe years to build something after the initial order. It then makes sense to send a Purchase Order so the building company can start building the product and the receiving company could place the order without having to pay for the product until delivery. But in the world of digital licenses, where it takes less than a second to generate a license, the same building/delivery issue doesn't apply and we prefer to keep things simple and deal only with payment cleared as a form of accepted payments.
Please go to Payment Options for a list of available payment methods.