Sierra FX30 Gateway Modem - Port forwarding

Hello everyone, I am using FX30 - IOT gateway in my application. As there is no user web page option provided for FX30 module for configuring port forward settings. I am trying to configure the port forwarding configurations in my gateway using iptables commands.
Here is my setup ,
1 end:

I have a ip device(192.168.104.xx) which is connected to FX30 gateway(192.168.104.YY) via ethernet (eth0) , now the tcp data received on eth0 with port number 2489 must be forwarded to public network(182.72.233.zz:2489) on rmnet0 (public cellular network).

2nd end :

At the receiver end (pubilc network 182.72.233.zz) the tcp data is collected by a server application and displays it on the console in a PC (in local network 192.168.104.aa).

How do i need to configure my iptables to achieve port forwarding : I have used below configuration but looks like i am missing out on some thing, any help would be appreciated

1.sysctl -w net.ipv4.ip_forward=1
2.iptables -A FORWARD -i rmnet0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
3.iptables -A FORWARD -i eth0 -o rmnet0 -j ACCEPT
4.iptables -t nat -I POSTROUTING -o rmnet0 -j MASQUERADE
5.iptables -t nat -A PREROUTING -p tcp --sport 2489 -j DNAT --to-destination 182.72.233.zz
6.iptables -t nat -A POSTROUTING -p tcp -s 192.168.104.YY -o rmnet0 -j MASQUERADE

Please help me figure out what is it that i am missing to achieve portforwarding

Thanks in advance !!