Go to roblox.com/redeem
Log in to your Roblox account
Scratch off the card to reveal the PIN if needed
Enter the gift card PIN in the redemption box
Click Redeem
Check your Robux balance or credit balance
If the card adds credit, use the credit to buy Robux in the Roblox website or app
If you have trouble, make sure the code is entered correctly and the card is not already redeemed