The "true" is not correct!
Try "false"! But: the registration will always be successful - but you will not trigger a call nor fetching an incoming call - thats my findouts from today (March 24, 2025).
BTW: I am trying to register to my Fritz.Box and to fetch then a incoming call. no luck at all --- currently.

Anyone else has a working test app?

 var sp = new SIPAccount(true, registerName, registerName, registerName, registerName, domainHost, 5060);