This content requires the base game XCOM 2: War of the Chosen on Steam in order to play.

https://store.steampowered.com/app/785300/XCOM_2_War_of_the_Chosen__Tactical_Legacy_Pack/

The XCOM 2: War of the Chosen - Tactical Legacy Pack includes a collection of new game modes, maps, weapons, armors, Photobooth options, and more that honors the legacy of the XCOM series.

Activating the steam key

1) You must download and install Steam http://steampowered.com/download/SteamInstall.msi (if not already installed).
2) Create a new account on Steam or go to an existing one.
3) Select "Activate via Steam ..." in the "My Games" section, and enter the key received after payment.
4) After activation, the game will appear in your list of games and you can install it.

Please leave feedback after successful activation of the game.