Hi there,
If you want to use the TRM500 as your internet source, you need a router that supports USB cellular modems and the TRM500 specifically, such as Teltonika’s own routers. Generic routers like UniFi UCG Ultra that do not support USB cellular modems will not work with the TRM500 connected via USB, regardless of their DHCP capabilities. The USB port, from information found online, is used only for power input, not for connecting usb modems or other data devices.
Regards,
Arturas