Processing interrupted transactions over non-persistent network connections

An offline retail machine, such as a point-of-sale terminal or vending machine, is designed to handle sales even when its internet connection is unreliable. It uses nearby mobile phones to send transaction data to a central server. If the first phone doesn't confirm the server received the data, the machine stores it and tries again with a second phone, bundling the original transaction with any new information, and only deletes the data once the server confirms receipt.