Does the link light come on, on the Internet port of the MX? Is there a reason why you're using WAN2, rather than WAN1 (not that that should make much of a difference)? Does the Inseego device provide DHCP to attached devices, sufficient to enable an MX to establish connectivity with the necessary Meraki resources in the cloud? I.e. - DHCP providing a valid IP address, subnet mask, default gateway and working public DNS server? Have you tested that with a PC connecting to the same port? Are there any firewall rules blocking traffic to the necessary resources?
Help > Firewall info in Dashboard or
https://documentation.meraki.com/General_Administration/Other_Topics/Upstream_Firewall_Rules_for_Clo...
Did you try accessing the Local Status Page of the MX, to see what it is reporting? https://documentation.meraki.com/General_Administration/Tools_and_Troubleshooting/Using_the_Cisco_Me...
Did you try factory resetting the MX? https://documentation.meraki.com/General_Administration/Support/Resetting_Cisco_Meraki_Devices_to_Fa...