Hi,
I tried to order a couple of pdfs this afternoon and wasn't able to. It sounds similar to the problem described here: http://paizo.com/threads/rzs2tj30?Purchasing-broken
I also tried to add a payment independent of the ordering process, but even though it said "payment added", it wasn't.
(Also, there's a UI issue: when I tried to add the payment on my MacBook, the address selecting popup didn't scroll down, so I could only choose my default address as the payment address -- which is the right address, modulo preferred vs real name)
Thanks for you help!