there are 2 codes, by the sounds of it you are using your 18 digit early access code. you need your 20 digit code that you get from the game its self or via e-mail if it was a digital version. But you cannot add a payment subscription unless you register your 20 digit code on the mog station.

The 3 day expiration time is for all of us as early access was extended by 3 days, you will be locked out of the game unless you register your 20 digit code by then (not 100% on this) then after you will get a 30 day extention.