To redeem a Roblox gift card, visit Roblox.com/redeem. This can only be done on the Roblox website, not on the mobile app or consoles. Make sure you are logged into your Roblox account.
If you have two-step verification enabled, complete this process to continue. Locate the PIN on the back of your physical gift card or in your email if it’s a digital card.
Enter your PIN on the redemption page and click “Redeem”. This will add the credit to your account. You can now use this credit to purchase Robux or a Premium subscription. Note that gift cards purchased from Amazon can only be used for Robux.
After redeeming, check your inventory for a free virtual item that comes with every gift card. These items change monthly and you can only get one per month per account. For more help, refer to the Roblox help article here.