My understanding is that your phone has to be using VoLTE in order for the conditional forwarding to work. In order for VoLTE to work you have to have it enabled in your account (which is probably true for everyone by now), and your phone have to be ...
Finally able to login and load the Change Subscription page but looks like the $34/40G is gone. It is still up on the main page so maybe there is still a chance.