There is a static route in the main router (192.168.2.0/24 via 192.168.1.30)
or
The wwan is moved to the wan firewall zone (or really any separate zone that has masquerading enabled.
In addition, the wwan network has been set with a static IP. Not shown in the picture is if the gateway and dns has been specified. If it hasn't, it also will not work.