Did not even know it required a registration code until I was prompted with this after downloading my game. I was told it was supposed to be emailed to me? Checked my e-mail, nothing there, have been trying to troubleshoot but can't seem to get it.
PSN never e-mails codes as part of Playstation Store purchases. I assume that you are referring to Final Fantasy XIV. There is supposed to be a system in place that will automatically entitle your PSN account on the game servers without the need for a code; although at launch it wasn't working 100% of the time. The codes are for retail copies of the game.
Here is a link to the starting tutorial (http://na.finalfantasyxiv.com/pr/start_ffxiv/ps3/). What they don't mention is that if you purchased the game in the Playstation Store, then no registration code is needed. Your entitlement is processed automatically when you purchase the game. Just skip that step, and move right to registration.