Static route - vs. inter-vlan traffic?

[Mark_Richards]

I have a client with a BR1 (older version with 2 ports) used to provide internet access to a single industrial supervisory device, which is plugged into the LAN port with the DHCP enabled as 192.168.51.1/24. This works fine.
There is 2nd independent network with its own sierra wireless cellular modem serving a dozen industrial devices on a 192.56.7.241/28 network.
The goal is to connect the peplink via the unused LAN/WAN port to the 2nd network (red line in the diagram) so the supervisory device can also talk to the devices on the secondary network. I added LAN/WAN port to the 2nd network with DHCP disabled. Using the peplink ping utility, a can ping devices on the second network, but cannot ping them from a laptop connected to the LAN port.
Do I need to define a static route? If so, what is the syntax?

Thank you.

[MartinLangmaid]

You need to set the BR1 WAN to be IP forwarding instead of NAT and add a static route to the Sierra Wireless router for the 192.168.51.0/24 network with a gateway of the BR1 WAN IP (10.56.7.252).

Then devices on the two LANs will be able to route to each other via their respective gateways.