[Users] How openser identify BYE within a DIALOG

Hi all, I want to know how OpenSER is able to identify the BYE that match a dialog. what are the essential header needed for the BYE message? I try to understand how work the acc module and what are the header needed in the BYE for generate accounting. My goal as i have wrote is to send a fake BYE to OpenSER and do accounting. In my test OpenSER correctly parse fake BYE and try to send the BYE to the UA, but don't send accounting info maybe i missing something essential for send acct. My fake BYE have: Via, Record-Route with ftag, To to-tag, From from-tag, Call-ID. i miss only the correct CSeq but i insert a custom CSeq like 9999. Any hints pls? :tele