How can I create and pay a bill from a purchase order without receiving it?

I purchased an item this week that requires a serial number. I will not have said serial number until I receive the item. However, the invoice has already been paid as the biller requires payment before shipping. But, when I try to convert to bill, I get the following message "The serial number value cannot be left empty. Please enter a valid input."

Every PO system I have used before would allow this, so I am assuming that I am simply not doing it correctly. How do I create this bill and mark it paid before the item is received?