Robux or Robuck is known as Roblox's primary currency on Roblox. Robux allows players to buy everything in the Roblox catalog with Builders' Club. There are several different ways Robux can be obtained or purchased, Roblox Promo Code is one of them. The promo code can be sent to your email when you Register Online on Robux page.

Which Payment Methods Do You Accept?
There are many ways to make a purchase on Roblox:
All major credit/debit cards - You can use a prepaid gift card to pay as long as you first register it with a billing address. For more information on prepaid cards, please click here.
PayPal - when selecting PayPal for a membership or Robux, you'll be directed to PayPal's website to login and complete your purchase.
Game Cards - Buy Roblox game cards at participating stores and online.  To see a list of participating retailers, please click here.
Rixty - Buy a Rixty card at a local gas station or grocery store. For a step-by-step guide, please click here.
Roblox Mobile App using iTunes, Google Play or Amazon - You can pay with iTunes or Google Play credit via the corresponding Roblox Mobile App. For more information, please click here.
Xbox - You can purchase Robux via the Xbox Live website or Roblox Xbox App for use on the Roblox Xbox App. For more information, please click here.

Roblox Promo Code for Robux Register Online click here

Builder's Club
Players who purchase BC, TBC or OBC receive a daily Robux stipend. Users in a Builders Club membership earn 15 Robux, while those in Turbo Builders Club or Outrageous Builders Club earn 35 and 60 Robux respectively. Players also receive a 100 Robux bonus for their first-time purchase of a premium membership.
Catalog Sales
Users can sell Catalog items such as T-Shirts, Shirts, and pants, to earn a profit, after Marketplace fees are calculated. (90% for NBC, and 30% for BC, TBC, and OBC.)
Game Development
Players can sell Game Passes and Developer Products to earn Robux in the same manner as Catalog items. Additionally, they can include gear on the game page, which will pay a commission to the developer every time a gear is purchased on that page.
1000 Robux Survey
Once or twice a year, the Roblox team do a survey in which you must answer around 50 or so questions. After answering these questions, you are redirected to a new survey in which all you must do is enter your Roblox username. After a couple of weeks, 25 random users get rewarded with 1000 Robux. Roblox Promo Code for Robux Register Online click here