Where is undead nightmare rockstar code for PS3?

I purchased the game Red Dead Redemption for the PS3, it included the DLC for Undead Nightmare. However, now when we put in the RDR disc it gives us the option to play Undead but asks us for the Rockstar Code, the code is NO WHERE in the packaging. Where do we find that? Are we having issues due to the Playstation Network still being partially down? Any help would be appreciated!!