I have set both subnets, 192.168.54.0/24 and 10.8.0.0/24 and this is no working yet.
I also set public address, although this is not published to the internet.
From freepbx server console i can reach 10.8.0.x subnet without any problem.
If i do
Asterisk CLI> sip show peers
extension look like this
15453/15453 10.8.0.9 D A 25646 UNREACHABLE
I achieved to set debug in this extension and make a call, you can see it here: textup loader .com/dgibf