Activating a Roblox key is really easy, just follow these steps:
1/ Redeem card in your account.
2/ Log into your profile.
3/ Go to the Game Card Redemption Page.
4/ Enter your PIN.
5/ Click on the "Redeem" button to add the credits to your profile.
6/ Your Balance will be displayed in green.
The key is not working
If you have activated the key according to the guide but the code appears not to work, please check what type of error message you receive and depending on it follow the appropriate instructions: