I need my content purchase to indicate my internal Purchase Order Number. How can I do that?

In order to have the purchase order included on the invoice, there is a special field that you can fill in when submitting the order in OverDrive Marketplace. When you click Purchase Cart on an order, a box will pop up that asks for Internal PO. Whatever you enter in that field will show up on the invoice in the “Purchase Order No.” box. The field is limited to 20 characters.