There are two ways to activate the Epic Games Key. The first is through the website and the second is through the application.

Activation through the website:

1. First, claim the purchased product on your Kinguin account.
2. Visit the epicgames.com website.
3. Sign into your Epic Games account or create a new account if this is the first game you activate on this platform.
4. Once you're logged in, use this link to activate your game.
5. Enter your key and click Redeem.

Activation through the Epic Games application:

1. Claim the purchased product on your Kinguin account.
2. Launch your Epic Games application.
3. Click on your account in the top-right corner and then click “Redeem Code”.
4. Enter your key and click “Redeem”.

Here you can check how to activate the key on Epic Games: