APM parse HTTP Connector json to message box, iRule etc.

Thank you for your answers, but i feel that parsing JSON data shouldn't be a problem according to this git project by pmscheffler where he uses HTTP Connector and json data collected with it:

sidebandauth/auth-iRule.tcl at main · pmscheffler/sidebandauth · GitHub

My problem is that i cannot get the data to variable in irule to first show the data in logs (log local0.) to be sure that I get the date i have this simple iRule

when ACCESS_PER_REQUEST_AGENT_EVENT {
    set id [ACCESS::perflow get perflow.irule_agent_id]
     if { $id eq "irule_agent_one" } {
		log local0. "iRule agent $id PRP."
                                                   }
    set log1   [ACCESS::perflow get subsession.http_connector.body ]
    set log2  [ACCESS::perflow get subsession.http_connector.status ]	    

    log local0. "Log1 $log1"
    log local0. "Log2 $log2"
}

But it shows error in ltm.log:

perflow variable name (subsession.http_connector.body) invalid (line 7)     invoked from within "ACCESS::perflow get subsession.http_connector.body "

and like i wrote before i  have a subsession:

879cb369./Common/HTTPConnector/XXXXXXXXXXX==.nvp_block.subsession.http_connector.body

The variable perflow.irule_agent_id shows in the logs so in my opinion its not like the variable is for example not yet populated?