I advise you to go here, click on the icon you want to add, press the code for that icon, then paste that into the icon field removing anything that isn't letters/text and then saving those changes. That should be the correct way of adding icons.
If you need further elaboration or demonstration, I'll be happy to provide them.
Also, please note if you attempt to do the same to pro icons and you don't have a pro account, that won't work.