As i understand you have 1 Rut240 registered on RMS .
2nd Rut240 (that is not registered on RMS) is connected on LAN of 1st Rut240 .
Now may be you are trying to access the second Rut240 on RMS with the help of 1st that is reg on RMS .
Yes, RMS has this functionality by which you can access the devices that are connected on the LAN of RMS registered device but you cannot see the data like reports/events/uptime etc and also you couldn't configure make changes on that device on RMS but you can access the webui of that LAN device and after accessing the device you can configure/monitor things on device WEBUI not on RMS.
But end device should support any of the following protocols:
RDP,VNC,HTTP,HTTPS and SSH.
As in your scenario the end device is supporting https,http and ssh protocols so this could be easily achieved :
Now go to your RMS account and follow these steps:
1)Go to RMS Connect on left side of the page.
2)Go to Remote Http.
There you will see the following window.
After adding settings you will be able to see the LAN device in Remote https/http page.
Then you will see the option to generate a token for the remote access. Then you can share/ save that link and whenever you want to access the device you can access through that link.
When generating link you will be asked for link/ token expiry also.
There is no port forwarding required for the remote access for the LAN device on Teltonika Router.
I hope it helps.
Have a good day.