Here you can buy the key The Walking Dead: 400 Days DLC (addition to The Walking Dead) at a bargain price. After purchase, you will immediately receive a key, activating which you will add DLC to the game The Walking Dead to your steam account.
Without the original The Walking Dead game on your account, you will not be able to activate the 400 Days DLC add-on.
https://store.steampowered.com/app/207620/The_Walking_Dead_400_Days/
You can activate the key in any region.
Steam