Asterisk+FREEPBX. Why does the call only go one way?

Question

Asterisk

Asterisk + FREEPBX without going outside in every sense of the word. Stands behind a router with a raised PPTP VPN server. Clients are the same android smartphones with the same firmware. As a softphone-zoiper, the VPNROOT program is used to connect to the VPN. As an IAX protocol.
Now the essence of the problem is that a couple of random users observe the following: registration is successful, a call comes to the user, but the user himself cannot get through to anyone, the PBX gives an answer as if the dialed number is not available. At the same time, the callback comes and after that it is possible for some time everything works in both directions, but for a rather short time.

Answer 1

Not enough information.
Asterisk version?
What driver is Asterisk running on? Have you tried turning off the canreinvite parameter for the peer? What is happening in the logs? Please post your peer settings.

Answer 2

Why does the call only go one way?

Crooked set up.
PS what is the question is the answer.

Answer 3

Perhaps the problem is from a crooked vpn to codecs, use sip. Client address and asterisk address on the same subnet?