oh , do you have clicked the "+" button on the left of the input bar?
Discussion
I clicked "+" and tried calling from here.
and nothing happened after clicked the call button?
It can call, but the other party doesn't know that you've called. They'll only know when the call stops.
so the other didn't received the call push notifications? May I know which phone he/she is using? I tried making a call and received a voice call notification, and you have to response within 1 min, or it will automatically disconnect