A method for authentication of coupons using a blockchain includes: storing transaction data for a payment transaction, wherein the transaction data includes at least a transaction amount; receiving an identification value; receiving a block included in a blockchain, wherein the block includes at least a block header and a plurality of transaction values, each transaction value including at least a coupon identifier and coupon data; executing a query on the received block to identify a specific transaction value of the plurality of transaction values where the included coupon identifier corresponds to the received identification value; and executing a query on the memory to update at least the transaction amount included in the stored transaction data based on the coupon data included in the identified specific transaction value.