AP Isolation

Either you have a typo or you have configured the device on the wrong network scope.

"1rst can't route to the ip. I have an i termal address  of 192.168.2.X and the the gateway gives me  192.168.12.X”

The 192.168.12.x/24 network is what the local LAN is working on. The 192.168.2.x/24 network will never communicate to the 192.168.12.x/24 without a gateway/router between the two. Configure all your clients to be on the 192.168.12.x/24 network. Just allow DHCP to provision the IPv4 address or static address outside the scope that the router provisions for. Any and all devices upon the 192.168.2.x/24 segment will only be able to see one another but not communicate to the 192.168.12.x/24 network. In order to communicate to the devices on the 192.168.2.x/24 net configure your device with an IP on that segment, ping one of the known clients on that segment and then once you know you can reach it make the appropriate application level connection to it. If the scanner only has a webUI interface use that to reach it and alter its IP address to the proper network. It will then no longer be reachable on the 192.168.2.x/24 segment but it will be where it needs to be. After devices are configured to the proper IP address rebooting or restarting them might be necessary. When the are configured on the LAN properly and their interface stands up it should ARP and be seen. If you dont see it right away ping the broadcast address of 192.168.12.255 and then look at the ARP table of your device.