I am making a SIP integration with RingCentral but I don't get the SIP messages that I would normally need.

What I am trying to do is an assisted transfer. Transfer to phone when answered.

I make a call from ring central custom sip phone A to ring central phone B. Then wait for the SIP messages to inform me that the B answered the call. But it doesn't work as expected. I get an immediate answer then it will play any audio as configured in the phone. Then it will make the call to B. So it seems that an intermediary sip endpoint is answering then passing that call to the actual phone.

What I need:
Some notification, a 183 SIP Session progress message or something like that would do the job. Just looking for some SIP message that says the call was answered by B not just that intermediate SIP endpoint that seems to answer the call immediately.