You need to go into Settings and then Store, and unlock it from there - it'll be available, there won't be a cost for it if it has unlocked. You then apply to the game, and if playing through Steam, you have to be online in Steam to access the Store, otherwise you get an error.
It had nothing to do with applying it, as i said, it wasnt unlocking. Turns out i was taking Winning the league as a cup comp. I unlocked it by winning champs league/super cup/domestic cup comps oer several seasons.