Openfire with VPN users

good day guys,
i need your support please according to the following scenario,

I have openfire server IP : 192.168.1.8,
i have pfsense server IP : 192.168.1.1,
and i have two Clients connected from the internet via the VPN
Client 1 IP : 172.16.10.2
Client 2 IP : 172.16.10.3
the Clients can login to the openfire they can chat and exchage photos and location
everything is fine, however when the Clients want to establish a voice call

if the users connected from 192.168.1.0 network , everything works
if the users connected from 172.16.10.0 network , it rings when i accept the call it shows connecting for 6 seconds then call is dropped, mentioning that 172.16.10.0 network is a virtual network for the VPN users and by test tools, they are ping eachother,
also they are able to explore the internet and able to access the resources of the internal network.

might you please help me
Thank you so much