If you intend to use the h900 4G router just to provide an Internet connection and router all traffic to the WAN port of your firewall then you will need to configure IP Passthrough.

This means that all traffic sent to the Internet IP address of the router will be passed-through directly to the firewall so in effect the Firewall has the Internet IP address.  In order for this to work you would need to use a Fixed IP SIM Card to enable traffic to reach the H900 router in order to be passed-through to your firewall.

STEP 1 - Configure your APN settings and Cell ICMP Check and confirm your router connects to your mobile network and has the correct public IP address.  The Cell ICMP will check the mobile connection to ensure it has not been dropped by the mobile network and reconnect if necessary.  3G/4G services are an always available service and not an always on service which means that the mobile networks will disconnect your 4G device at some point and the Cell ICMP check is the mechanism to monitor this.

once you are happy with the Internet connection then follow the instructions below.