How to properly forward/redirect calls with pjsua2 - pjsua2

Question

I can't find info on the net how to forward a call with pjsua2.
Currently Im trying with the xfer method but Im getting:
../src/pjsip-ua/sip_inv.c:3942: inv_on_state_null: Assertion `!"Unexpected transaction type"' failed.
There is no information about this error.
This is my code Im trying:
void MyAccount::onIncomingCall(OnIncomingCallParam &iprm)
{
MyCall *call = new MyCall(*this, iprm.callId);
...
calls.push_back(call);
...
QString fwd_to = fwd(QString::fromStdString(ci.remoteUri));
if(fwd_to != "NO_FWD")
{
info+="*** Xfer Call: ";
info+=QString::fromStdString(ci.remoteUri);
info+=" [";
info+=QString::fromStdString(ci.stateText);
info+="]\n";
infoChanged=true;
CallOpParam prm1;
prm1.statusCode = (pjsip_status_code)200;
call->answer(prm1);
pj_thread_sleep(2000);
CallOpParam prm2(true);
call->xfer(fwd_to.toStdString(), prm2);
}
else
{
// standart incoming
...
}
}
fwd is my own function which search a database if it needs to forward the call

Answer 1

I did something like this and works, dont know if some other way exist:
(answering with no media, setting flag and in other thread xfering call to fwd_to string)
if(fwd_to != "NO_FWD")
{
CallOpParam prm1;
prm1.statusCode = (pjsip_status_code)200;
call->answer(prm1);
call->fwd_to = fwd_to;
call->fwd=true;
}
FwdThread *fwd_thread = new FwdThread();
fwd_thread->start();
void FwdThread::run()
{
static pj_thread_desc s_desc;
static pj_thread_t *s_thread;
pj_thread_register("FwdThread", s_desc, &s_thread);
loop();
}
void FwdThread::loop()
{
while(1)
{
for(auto &call : pjt->v_calls)
{
if(call->fwd && call->answered)
{
call->fwd=false;
CallOpParam prm2(true);
call->xfer(call->fwd_to.toStdString(), prm2);
}
}
if(pjt->Stop)
break;
pj_thread_sleep(500);
}
}