Mikrotik port forwarding. SIP telephony?

Question

SIP

Good afternoon! Help please solve the problem.
There is a remote telephony server to which Mikrotik is connected via Ipsec VPN.
There is an office with employees, which is also connected to Mikrotik via an OpenVPN server.
The office worker starts Softphone and tries to connect to the telephony server.
Path: Openvpn client ---> Mikrotik OpenVPN server --> VPN Ipsec telephony server (external).
There is access to the telephony server from the openvpn client side (ping, telnet to port 5060, etc.), but there is no access to the openvpn client from the server side (so the telephony server administrator says). He asks to open ports on Mikrotik towards openvpn client 5060-5061, 5070-5090, 5100-20000.
I can't figure out how to do it.
How to forward these ports through Mikrotik from the telephony server to the client with a softphone?
About 20 people will connect to this telephony server.
Telephony server interface on Mikrotik: ATC-SIP, IP: 172.12.0.10
Telephony network: 172.12.0.0/23 Openvpn
server IP client pool: 172.21.108.0/24
How to forward ports from 172.12.0.10 to 172.21.108.0/24?
Disabled the SIP helper/ip firewall service-port disable sip

Answer 1

Solution found. Used GRE instead of Ipsec and everything started running...

Answer 2

I can assume that there is NAT along the way, most likely even in two places Openvpn client ---> Mikrotik OpenVPN server. Set up l3 routing between all of this.