UPDATE3
North American site is bugged and is issuing EU codes (beginning with RAAE). Still no news or resolution from SE. Hang tight.
UPDATE4 -
https://twitter.com/FF_XIV_EN
We sincerely apologize, but the pre-order redemption site is experiencing very high traffic which we are currently working to resolve. We are adding additional bandwidth and server capacity to ensure that all customers will be able to redeem their pre-order codes as soon as possible. Early Access starts on August 24th at 2am PDT, and Square Enix is working hard to ensure that all #FFXIV pre-order customers will be able to download and play the game.
UPDATE5 - PackOfHighly
Thank you for submitting the information. We are currently aware of this issue and we are investigating the cause. We are going to escalate this matter to be looked into and we ask for your patience regarding this as look for a resolution. Unfortunately, I don't have an immediate resolution but we are looking into the matter. Please keep attempting to use the code on the account while we look into the issue at hand. Keep checking your e-mail for any updates and check the twitter page for FINAL FANTASY XIV for any announcements.