The Lock Box is a special promotion which only appears for players who have never made a purchase before. If you have a Lock Box promotion available for your account, you will see an icon for it on your home screen or on your store page.
If you have a Lock Box available, each time you use Favor Points in-game, a portion of them will be saved inside the Lock Box. When you're feeling low on FP, you can spend a small amount of money to crack open the Lock Box and receive all the FP inside, plus an added bonus!
Players can currently open their Lock Boxes three times. Once they disappear from your account, you won't see them again!