Function dpiMsgProps_getPayloadJson 

pub unsafe extern "C" fn dpiMsgProps_getPayloadJson(
    props: *mut dpiMsgProps,
    json: *mut *mut dpiJson,
) -> c_int

Returns the payload associated with the message properties, The payload must be a JSON object and is available after the call to dpiQueue_deqOne() or dpiQueue_deqMany(); otherwise, the value NULL will be returned.

The function returns DPI_SUCCESS for success and DPI_FAILURE for failure.