By default (at least on Ubuntu) a non-root user has no permission to access the ttyUSB* ports. So if you have Domoticz running under a separate user (which is always a good idea to make the system more secure), Domoticz isn’t allowed access to your RFXCOM for example. Here are two methods of doing it. For most people the first one by adding the user to the dialout goup is enough and by far the easiest.
This can be done by running the command below:
sudo usermod -a -G dialout YOURUSERNAME
(Where you replace YOURUSERNAME with the user that runs Domoticz.)
