A managing platform for appending supplemental payment data to a transaction message receives a transaction message representative of a credit card transaction from a merchant or an associated financial institution. The managing platform uses the transaction data contained in the transaction message and other information to determine whether the transaction satisfies one or more payment rules previously established by the cardholder. If the transaction satisfies a payment rule, the managing platform appends supplemental payment data to the transaction message in a format specified by a financial institution associated with the cardholder. The supplemental payment data includes information identifying a secondary payment account associated with the satisfied payment rule. The managing platform subsequently transmits the appended transaction message to the financial institution associated with the cardholder.