In the 3102 WAN settings. Don't use DHCP. For some reason some of the settings, netmask, gateaway are all zeros! Set the IP to Static , Put in the static Ip you already have put in 3CX for the gateway (192.168.0.64) the gateway, usually the IP of your router (192.168.0.2?), a netmask, usually 255.255.255.0. If your router is at 192.168.0.2, then leave i the IP as the Primary DNS server.
In the LAN setup tab, change NAT to Bridge. You've put the IP you want the 3102 to use on the WAN port in there, you can change that to something like 192.168.1.1).
Make sure you are plugging your network into the WAN (internet) jack. Once you have set the LAN settings to Bridge, you can then use the internet port to lug in another device for your network. Setting to Bridge disables the router function of the 3102.