How to use the WAN address in Nftables custom rules?

Hi,

I'm tryining to add NAT reflection rules for additional zones in fw4 to workaround this issue.

For that, I'm creating my rules in /etc/nftables.d/nat_reflection.nft. However I need to use the WAN address in the rule but I don't know how. I see that there are some variables defined like $wan_devices and $wan_subnets. Is there any way to get the current IPv4 WAN address?, also, any way to filter the subnets to get only the IPv4 one?

My rules look like:

chain user_dstnat {
    type nat hook prerouting priority dstnat; policy accept;
    iifname $lan_devices ip saddr 192.168.10.0/24 ip daddr $WAN_ADDRESS tcp dport 80 dnat ip to 192.168.7.5:80 comment "!fw4: forward-http (reflection for lan)"
    iifname $lan_devices ip saddr 192.168.10.0/24 ip daddr $WAN_ADDRESS tcp dport 443 dnat ip to 192.168.7.5:443 comment "!fw4: forward-https (reflection for lan)"
}

Thank you.