A method for routing computer messages between parties is provided. The method is implemented using a message gateway computing system including a processor and a memory. The method includes receiving a message routing offer from a seller and a representing an offer to process payment card transactions. The method also includes receiving a message routing request from a buyer. The method further includes first message route between the buyer party and a first seller party of the plurality of seller parties on a message processing network. The method also includes receiving a payment card transaction from the buyer party. The method further includes identifying the first message route associated with the payment card transaction. The method also includes transmitting the payment card transaction to the first seller party based at least in part on the first message route.