I originally purchased ff14 ARR through steam. made my way into gamestop one day to get rid of some old games. I was not originally going into gamestop to purchase heavensword, I was going to sell old games and get some cash or credit.
I purchased the heavensword ce I guess retail version (which at the time I didnt even know there was a difference between the steam and retail versions).

After finishing all the quests in ARR i went to the mog station to put in my code on my receipt (which is a 20 characters long CE code) but it says that the code is invalid. I tried activating my product on steam, and I tried entering my code into the pre order code screen in mog station instead of the expansion code screen.I found a couple solutions online the first being: steam version and retail version are different, have to re purchase through steam. Second solution was that the person just kept entering key and it eventually worked.