An applications programming interface (API) or other interface may be configured for use with a plurality of e-commerce applications and/or a plurality of payment systems. The API may be associated with an operating system of a client or may be otherwise located in an e-commerce system or network. The API may receive a call regarding a purchase transaction. The purchase transaction may be examined to determine if a payment method is synchronous or asynchronous. An appropriate payment system may be activated to perform the purchase transaction based at least in part on the determination made by the examination of the purchase transaction. A result of the purchase transaction may be sent to the e-commerce program. By revision of the API, developers of e-commerce applications are freed from the burden of revising code in response to the need to utilize additional or differently operated payment systems.