Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for processing payment events. One of the systems includes one or more processing engines configured to periodically retrieve information from a payment event feed that comprises a list of payment events in an order, and a server configured to perform a sequence of steps for a payment transaction, the sequence of steps including receiving a request for authorization of the payment transaction from a merchant, receiving an indication that the payment transaction has been authorized, and sending authorization to the merchant for the payment transaction without receiving acknowledgment that the one or more transaction processing engines have received the request for authorization, wherein the server is configured to record completion of each step in the sequence of steps as a payment event in the list of payment events to generate the payment event feed.