A simple DRS device just needs to be able to make outbound web service calls to a few DRS end points in order to place a order and update status. This implies that you do not need to be able to tie SNS notifications back into the device in some manner.
The one use case that seems to cause a problem is when the customer cancels the order. The CX guidelines detail receiving the cancel order and then reordering in 5 days. A 2nd cancel stops future orders. It seems you have no way to implement this behavior without the SNS notifications. None of the end points provide order status at this time.
Is this a real requirement ?
Am I missing another way to deal with this ?