Shift Codes Borderlands 3

Question. I just redeemed 5 keys to borderlands 3 but when I enter the game and go to the mailbox to collect those 5 keys, there not there. Why is this?

Thank you.

Are you sure it was for BL3? Sounds like the code was for different game.
Check here https://shift.gearboxsoftware.com/rewards
Also every BL3 code is posted in this topic Updated shift codes