Did you figure out an answer to this?
I've been able to place orders by creating a listing with the autoPay payment policy set to false and then using a sandbox buyer account to navigate to my listing and buy it now then "commit to buy". I can't actually get a payment to work, but it will create an order than can be accessed via the Trading API. Unfortunately, I can't figure out how to get fulfillment API to show orders in sandbox.
