How to activate key on Rockstar Games Launcher?
1. Go to Rockstar Games Website.
2. Log in to your account. Click on Profile icon in the top right corner of website. then click "Sign in" and enter your credentials.
3. Go to Activation Page. Click on your avatar in the top right corner of website. then click "Game Activation". Click "Use Rockstar Code" next to the game you want to activate.
4. Enter your key. Enter your key and click "Activate".
5. Confirm your product on the next page by clicking purple "Confirm" button.
6. That is it. Now you have the game in your Rockstar Games account's library.