I have the mage outfit season 8 and it won't let me equip it... It says I don't have a base outfit... what do I do in these cases?

Unless you've previously used the season 8 base outfit scroll any season 8 addon mage/ranger or warrior scroll is useless for you...

Understand that the Season 8 outfit scroll was originally a one-time reward and was not supposed to be split, but it was divided into 3 stages only to be fully claimed.

The player needed to reach level 300 to unlock the base outfit & first addon scroll, and reach the other two addons at levels 400 and 500.

So if someone sold you just an addon without the base outfit, they were probably dishonest with you, since the scroll is named 'addon', there's no other addon scroll in game, but like it or not, an addon scroll inherently presupposes the existence or necessity of another scroll without 'addon' in the title...

A simple search in the Library -> Items -> 'season eight...' and half of a brain to think: ''ohhh so there's also a base outfit, maybe I need it in order to use the addons later...'' and you would have avoided this problem to yourself. Good Luck, bro!

I think you were the victim of a scam O.o
Or a small piece of unclear information, probably intentional

Request the cancellation of the deal and call for "Celso Russomano".