It's not on MogStation, it'll be on the same page you got your Early Access code from, through the SE Store. https://store.na.square-enix-games.c...ccount#/orders, click on "See Unlocked Key" and it should be under the EA code. Not sure about Steam, I assume that's under the unlocked Steam keys, and for ps4/ps5 it should be automatic upon logging in, from what I understand.

If the code is not there, check periodically or wait to see if you get an email from the SE Store. I checked at midnight and didn't see the code, but about a half hour later I had it in my inbox for this morning. They're likely being sent out in waves, so you'll get it soon and well before the Dec. 10th cutoff.