Here is what we have so far: we can successfully pull the cart from the API.
We can also successfully update the cart billing/shipping addresses as well as the shipping method.
The problem arises when we try to create an order via POST http://store.allsportstshirts.com/SaveCartOrder/95627/{SessionID}.
The data we are sending with that request is the following:
payment_method: Credit Card
cc_num: 4242424242424242
cc_exp: 03/23
cc_cvv: 123