@Ananda, the error is saying you must subscribe before adding an additional computer. You must have a computer in your account already. If you delete it, or subscribe, you won't get this error.
The subscription allows you to have more than one computer, and run more than one command per minute.
@rexabbot, no, but if you want to run foreground commands that launch GUI application like a browser, you can open a terminal window within X-Windows, and run triggercmdagent. That will run the agent in foreground mode.
Unfortunately you won't be able to use the GUI editor though, so you'll have to edit the commands.json file manually with vi or pico.