Roblox Gift Cards can only be used online at Roblox.com/redeem; they cannot be used on any video game console or the Roblox mobile app.
There are two types of Roblox gift cards:
Credit is the actual value of Robux or Roblox Premium Memberships that can be purchased. Credit is sold here.
Robux is a virtual currency that is added to the account balance and is only available at Amazon.com’s Roblox Store.