Dynamically enabling and facilitating businesses or other entities to locate and transact with payment systems for the purpose of processing payments. A customer interacts with a supplier of an item (e.g., goods or services), selects an item for purchase, and provides the supplier with payment criteria. The supplier queries a payment system directory to locate candidate payment systems for the transaction. The supplier then interacts directly with one or more of the payment systems to partially or fully process payment for the transaction. Alternatively, the supplier interacts with a gateway service, which queries a payment system directory to locate candidate payment systems and then interacts with one or more of the payment systems to process payment for the transaction.