Abstract: An interface and device architecture for a payment device. An interface between a payment application installed in a payment device and one or more value-add applications (such as loyalty programs, transit applications, etc.) that are also installed in the payment device. The API or interface design permits communications and data transfer between the payment application and one or more value-add applications. This reduces (and in some cases may prevent) the need for back-end server processing of data that may be relevant to both a payment transaction and to a function of the value-add application. Similarly, the same or another API or interface may enable communications and data transfer between a value-add application and the payment application.