In one example, a server system facilitates an exchange of messages with a remote client application. An Application Program Interface (API) receives a first request message and a second request message, wherein the first request message includes a first data payload defined by a common definition and including a first payload data, the first payload defined by a first schema definition. The second request message includes a second data payload defined by the common definition and a second payload data, wherein the second payload is defined by a second schema definition different than the first schema definition. In response to receiving the first request message, the API transmits a first response message, and in response to receiving the second request message, the API transmits a second response.