i have installed lora gateway bridge on ubuntu. its ip address is 192.168.8.100 should i configure this in loalconfig.json or should i use other address.
If you gateway is on the same local network, then yes, you should use that address.
If you gateway is on a different network (or a mobile data plan), that will not work because the 192.168.x.x one is a private reserved subnet which cannot be reached from the outside world.
And if your gateway is the same computer that is running the gatway bridge, you would probably want to use the loopback address 127.0.0.1 instead.