So, I'm trying to figure out this plugin, and I found a tutorial for the right version of it (I had been using the older commands), and with both I got a "too many arguments" error when using the commands from the console.
The tutorial instructed me to enter a couple of commands to add an admin group, then add myself to it. I entered /pex group admin def true, and that did work, but I got the error when I entered /pex user [my username] parent add group admin.
I'm running (well, setting up) a modded MC 1.10.2 server.

I forgot part of the command. Wow.