Why does an IP phone not work through OVPN between two Mikrotiks?

Question

SIP

OVPN is configured between two mikrotiks. Behind the VPNServer is a PBX. Behind the client is an ip-phone.
The IP phone connects to the PBX without any problems.
When calling to this phone, the voice of the caller is not heard (dead silence), but the user is heard well by the phone.
What could be the problem?
At first I thought that the problem was in the firewall, but there is not a single rule.

Answer 1

Try to disable (or enable) SIP helper (ip firewall service-port, SIP will be there) in the Mikrotik settings.

Answer 2

Because OVPN on Mikrotik is shit. UDP traffic does not go there. Replace this blasphemous tunnel with PPTP\L2TP and best of all EoIP inside PPTP\L2TP and you will be surprised by the result.