3D PUZZLE - Underground has invalid key. 'The product code you've entered is not valid or is not a product code. Please double check to see if you've mistyped your key. I, L, and 1 can look alike, as can V and Y, and 0 and O. '
Steps to redeem the key:
1. Download Super Squad on Steam and open the game.
2. Go to the in-game store.
3. Enter your code in the "Promotional Code" box and hit "Redeem".
Good luck and have fun.