DarkSiders

Is it a key? I don't know what you're asking

To Redeem:

1. Visit gamestop.com/redeem and enter the code along with the email address associated with your GameStop PC Downloads account. If you don’t already have one, you can sign up for one for free.
2. Download the free GameStop PC app if you don't have it already.
3. Open the app, log in with your GameStop PC Downloads username, and click on the 'My Games' tab to download the game.
4. Once the game is downloaded, double-click on the name of the game on the 'My Games' tab to begin playing.

Steam>Activate a product on steam>Next>Next>Key>Next

If you're talking about that gamestop one then add it to your gamestop app and click 'Product Code'. You'll get a valid Steam code.

1. go your gamestop app account and reedem your key in the mail

2. go gamestop app's libery and see product code

3. copy product code and active it on steam

Instal Gamestop app, log in, go to my games, and if you redeemed the code on your email you are going to get the game on gamestop library, and then search in the game for product code, copy and paste to your steam account and you are ready to go.
Worked for me today and i can check this option.