Alright but dont you need to use http://preorder.eu.finalfantasyxiv.com/gb to turn the 6-3-6-3 into a 20 digit code first?

Its very confussing, assuming you dont have a SE account already, i would assume you'd have to make a account first then convert code to 20 digit, then add via mogstation by adding bonus code

then add game registeration code to turn account into a proper account with +30 days game time.