X4: Foundations | GL

Launch the Steam client and sign in to the account you want to add the game to — once activated, the key is permanently bound to it.

In the client's top menu, open the "Games" section.

Select "Activate a Product on Steam…".

Click "Next", accept the user agreement with the "I Agree" button, enter the key, and confirm — the game will appear in your library.

Via browser: open store.steampowered.com/account/registerkey and sign in to the same Steam account.

Enter the received key in the field on the page and confirm activation — the game will be added to your library, and you can download it through the Steam client.