Hello. I’ve been away and you may have solved this already.
The CorrelationID in request/response is used to map the response to the original request. solClient_session_sendRequest automatically sets this to a easy to parse but unique string (#SOLnnn) for each request. Then the sending session can easily and quickly, which is the important part, scan all incoming messages for the response to the request.
_solClient_session_sendReply automatically retrieves the correlationId from the request message, and the reply-to topic, and populates the reply message with these values so the reply get to the right place.
The application cannot override correlationId, and if it were able to do so, request-reply would not work.