'This content requires the base game Grand Theft Auto V on Steam in order to play.' Or, are you wanting the CESP for a 'different' social club account/game copy? Does R* no longer sell the CESP by itself to those with old/'standard'/not premium copies from R* store/warehouse/ingame anymore?
Looks like you got a mouse icon by your name - so you do infact have Gtav on steam (edit - and achievements from today to back that up).
