Go here and log in to your Epic Games account.
Hover over your name in the top right corner, and then click V-Bucks Card.
Click Get Started to begin the redemption process.
Enter your PIN code with no dashes.
Select the platform you want to redeem the V-Bucks Card on, and then click Next.
Review the details and make sure the Epic account, device, and new balance are all correct, and then click Confirm.
To install this Web App in your ISO device press and then Add to Home Screen.