# Set the player's list name when they are AFK. This is none by default which specifies that Essentials 
# should not interfere with the AFK player's list name.
# You may use color codes, use {USERNAME} the player's name or {PLAYER} for the player's displayname.
afk-list-name: &7[AFK] &o{USERNAME}

^It claims that I can't do that when trying to make it.

Sorry about the massiv text

Can you please not use unnecessary headings like that. It is irritating.

Try:

afk-list-name: '&7[AFK] &o{USERNAME}'

In YAML if you start with one of many symbols, including & you need to actually use quotations, single or double.

P.S. the massive text is because you used #.

Edit: I edited your post to wrap all of the config content into code blocks using three backticks `

Silly me, sorry about that.