This seems to happen pretty infrequently, for the most part our FB credits callback seems to work fine, but every so often we'll get a "placed" callback for an order, but never a "settled". From the user's perspective, they hit the confirm button and the credits are removed from their account, and then no product is delivered, usually leading to us getting an angry complaint. When we investigate, we find no errors on our FB callback server, and can see the initial "placed" message coming in, but never the "settled", and since we only deliver product on a "settled" from FB, the product is never given.
This seems to happen very rarely, and in at least one reported case the user says that they had to buy more FB credits in order to complete the transaction.. is there some difference in status that occurs when this happens? Does Facebook not capture the funds right away in this case? Has anyone else seen this happen?
In fact the "settled" status was deprecated, you need to attribute the product on the "placed" callback.