A transaction processing and authorization service. If a source entity does not respond to an authorization attempt via a communications channel, the service may generate a transaction phrase corresponding to the transaction and communicate the transaction phrase to the source entity. The transaction phrase may also be stored by the service and associated with the source entity's account and the particular transaction as initiated, and may be used to identify the transaction. After receiving the transaction phrase, the source entity may then, if desired, return the transaction phrase to the service. Upon receiving the transaction phrase from the source entity, the service may then contact the source entity via the communications channel to authorize the transaction. As an alternative, a source entity may submit a replay command to the service to replay any pending transactions.