How to Allow all NATed traffic from iptables firewall via pfsense (gateway)

I have an iptables firewall (machine 1) and a centos 7 based gateway (machine 2), which is having 2 interfaces (machine-2:int-1) from WAN [/30] and (machine-2:int-2) is LAN [/28] one of the static IP provided by ISP. Now this setup is working fine, machine-1:LAN-subnets are doing iptables based NATing and machine-1:LAN-subnet-int's gateway is machine-2's:int-2. All routes for NATed IPs gateway are set as iptables firewall.

LAN
   ^
   |
   |
FIREWALL (NAT) --> Other int's *-- IPTABLES
   ^
   |
   |
GATEWAY (no NAT) *-- PFSense
   ^
   |
   | 
  WAN (ISP)

Now I would like to replace the CentOS based gateway with PFSense. As soon as I replaced the Gateway machine with PFSense, NATed addresses are not passing thru. I tweaked the NAT outbounds rules, disabled it. Still I could not make this happen. I need to make rules and routing in PFSense, that allows all the traffic from LAN to WAN as is (no NATing - since iptables firewall is taking care of it). Please suggest.