Hi, can you try to see if Teltonika router has internet connectivity by doing a simple ping test to any host on the internet? I'd recommend pinging a hostname to verify both internet connectivity and hostname resolution (try to ping google.com / youtube.com / facebook.com if mobile network is not restricted).
If hostname resolution fails - try to ping some commonly used IP address directly (126.96.36.199 / 188.8.131.52). If that fails - double check if Teltonika router itself has default route (do ip route via CLI and check output - there should be a default route there).
If hostname resolution and internet connectivity is working on Teltonika router - do these hardcoded devices have default gateway set? If not - it won't be possible for these devices to route packets towards any network other than its own broadcast domain. You'll have to set default gateway on these devices.
Also, just as a general thing, try to validate if LAN connectivity is possible between Teltonika router and your end devices. That might be a thing worth looking at as well.