APM 401 Response Settings | Adding SessionID Variable

Hello!

I am trying to capture the current session ID when the "http 401 response" negotiation fails. I added a iRule and applied it to the Virtual Server the following command:

    when ACCESS_SESSION_STARTED { 
            set sessionid [ACCESS::session data get "session.user.sessionid"]
    }

In the APM HTTP 401 Response object, I added %{sessionid} in the "HTTP response message"

Unfortunately I am not getting getting a value from it.

Please advise

Thank you

J