There should be 3 network ports on your Peplink BR1 Max Mini LTE HW3.
There should be a cable connecting the Peplink LAN-1 port to the Araknis network switch, with the digital menu boads also connected to the Araknis switch.
The POS equipment should be connected with a cable to the Peplink LAN-2 port.
Nothing should be connected to the Peplink LAN-3/WAN port.