Having looked into this problem a bit yesterday, it looks like Amazon's client for connecting to their payment system can error out in any number of ways, and they recommend that you just try again. We had been handling all of the different kind of payment statuses that they can return but hadn't been expecting obscure errors to occur in the normal flow of operation that would also need to be handled as possible successful payments. In any case it won't be hard to fix the particular problem that you encountered a few days ago. Unfortunately, Amazon is phasing out this whole payment system in six months, and there will undoubtedly be a fresh batch of issues to address with whatever the next payment system we integrate ends up being.