An important difference between the two is that the Mapped convention returns a service fault if a virtual service is configured for application/json (Mapped convention) and it encounters a message that has namespaces, while the Badgerfish convention attempts to avoid losing any meaning encoded in XML by preserving namespace declarations. The Axis2 JSON library MessageFormatter will complain if Mediator attempts to transform an XML response that contains namespace declarations. So, either make sure that the requests do not include namespaces, or else set the MESSAGE_TYPE to application/json/badgerfish instead of setting it to application/json.