Thank you, @viragomann.
I think I spoke early. I am having issue with connection / sound. I created a rule on LAN:
Protocol IPv4 *
I also replicated all the outbound NAT for the FREEPBXVPNINTERFACE. When I checked the States I am getting CLOSED:SYN_SENT and SYN_SENT:CLOSED
If I change the Gateway to GCPVPNINTERFACE_VPN4 I got ESTABLISHED:ESTABLISHED. I compared Both Gateway and they look the same.
If I ping the FreePBX server as FREEPBXVPNINTERFACE I got 100.0% packet loss. If I ping the FreePBX from my computer (or GCPVPNINTERFACE) I got 0% packet loss
It looks like the FREEPBXVPNINTERFACE / Gateway is not passing the traffic. Any idea on how to troubleshoot this?