As you just mentioned, A key has been shown and sent to his mail box. He tried to put it straight on to the mogstation website by using the ''add platform'' button but it said that the key was invalid.
So he went on this
https://secure.square-enix.com/accou...?rgn=eu&lng=fr link, followed the steps and it worked... then he had 2 days to put the game activation key,
which he never received =/