receiving, by a transaction management controller and from a business management engine, a transaction amount for a payment transaction, the payment transaction based on a purchase transaction initiated by a point-of-sale (POS) device of a merchant-specific environment, and the transaction amount for insertion by the transaction management controller into a payment authorization request message;

requesting, by the transaction management controller and from a card reader of the merchant-specific environment, payment card data for the payment authorization request message, wherein the business management engine and the POS device are communicatively isolated from the card reader;

receiving, by the transaction management controller and from the card reader, the requested payment card data for insertion by the transaction management controller into the payment authorization request message;

inserting, by the transaction management controller, the payment card data received from the card reader and the transaction amount received from the business management engine into the payment authorization request message;

transmitting, by the transaction management controller and to a payment network, the payment authorization request message;

receiving, by the transaction management controller and from the payment network, a payment authorization response message for the payment authorization request message; and

transmitting, by the transaction management controller and to the business management engine, the payment authorization response message.