Make sure you're on the default factory settings and your DNS address hasn't been changed.
The next step would be looking if you have default WAN set as an active interface which also resolves DNS correctly. If there's something in the gateway blocking the address - it also might cause this issue. So for this, I would recommend using a mobile interface as your main WAN.
Also, make sure the port for rms.teltonika.lt is 15009.