Unable to get Main and Backup Routers to connect to each other

I have two networks and routers (both on Advanced Tomato by Shibby) laid out as such:

1. Backup Router network (192.168.1.1/24)
   1. WAN - Xfinity
   2. LAN - small number of clients. Importantly, main network router is a client on this network.
   3. Network interfaces
      1. br0 - local
      2. eth0 - Xfinity
      3. eth2 - Wireless network - this is the network on which the backup network is connected as a Wireless client
2. Main Router network (192.168.2.1/24)
   1. WAN - Fiber
   2. LAN - Connected to mesh networking access points. Almost all of the devices in the house are connected via these Mesh networking access points to the main network. Especially important are my local NAS, and services hosts e.g. Plex, Printers and Gaming desktop.
   3. Load balancing - This router is a "Wireless client" on the backup network router, and has Multi-WAN with load balancing enabled.
   4. Network interfaces
      1. br0 - local
      2. eth0 - Fiber
      3. eth2 - client on Backup network with IP 192.168.1.81

How it's working: As long as the client is on the main network, the system works well. They are able to access the NAS, printer etc. They are also able to access and ping any client on the backup network.

Problem: The problem happens when the client is on the backup network. The clients on the backup network aren't able to reach the NAS, printer etc on the main network.

What I have tried: I have tried to allow the backup router to enable it's clients to reach the main router network. I found a few articles mentioning doing this and performed the following steps:

1. I have tried adding the following iptables forwarding to Backup networkiptables -I INPUT -i br0 -j ACCEPTiptables -I FORWARD -i eth2 -d 192.168.2.0/24 -j ACCEPTiptables -I FORWARD -i br0 -d 10.9.8.0/24 -j ACCEPT

2. Enabling ip packet forwarding on BOTH backup and main networksBy running echo 1 > /proc/sys/net/ipv4/ip_forward

3. Add ip routeip route add 192.168.2.0/24 via 192.168.1.81

Issues - Unfortunately, this is not working. When I try to ping 192.168.2.1 from my backup network router, I am getting the error - Unable to ping From 192.168.1.1 icmp_seq=1 Redirect Host (New nexthop 192.168.1.81).

My guess is I am messing up on the iptables part. I do not fully understand what I am doing there. If someone can please help, I would deeply appreciate it.