Updated on September 22, 2021
Money orders are used to send transactions between two accounts in a rollup. The transaction process is performed in two steps: the sender creates the money order, then the recipient redeems it. A money order can only be redeemed once stored onchain.
An operator stores money order batches in memory as a sparse Merkle tree (SMT) before sending the batch onchain. An SMT contains the money order batch root hashes that have been added to the rollup.