Hi Andzej, thanks for your reply. I really appreciate the help.
I messed up a little bit with the route settings on ZeroTier website, since i reset the TRB140 a couple of times to start all over, and then forgot to edit the route to the new IP of the trb. Anyways, I think I corrected that now. Now I can ping both the TRB and the LAN ip (10.0.0.5) of the trb from the remote PC. Great!
But I can't ping the IP of the device (PLC) connected to the LAN port of the trb (10.0.0.10). Do I need some firewall / port forward settings for this to work?
PS. I read a guide about settings in Firewall > Port Forwards, which mentioned the parameters: Protocol, Source zone, External port, Internal zone, Internal IP address and Internal port. But I just see the parameters: Name, External Port, Internal IP address, Internal Port, so the guide is difficult to follow. I am running the newest firmware on the trb.