You can only invoke an asynchronous Web service request as a procedure using the RUN statement. This means that if a Web service operation is invoked as a user-defined function, you can only invoke it synchronously, because all operations that have a return value can only be invoked as user-defined functions, where the value must be made available at the point of invocation. This is consistent with how OpenEdge supports the invocation of asynchronous requests on the AppServer (remote procedures only).