A method of processing a purchase transaction includes generating a transaction file containing a product code, which is transmitted from a user computing device when an image of a product code identifier is captured by the user computing device, a first user ID of the customer, and an indicator of whether or not the customer has opted in to receive electronic receipts. The method further includes generating an electronic receipt based on the transaction file, storing a conversion table containing the first and second user IDs of the customer, converting the first user ID contained in the transaction file to the second user ID based on the conversion table, when the indicator indicates that the customer has opted in, and storing the electronic receipt in association with the second user ID. The electronic receipt is transmitted in response to a request for electronic receipts associated with the second user ID.