What are the different types of challenges?

There are 2 different types of challenges. 

• Free challenges
  These challenges offer no monetary reward, only personal improvements and a place on the challenge leaderboard.  Some of the free challenges are automatically added for you and some you need to sign up for manually. Once a challenge starts, you only need to have your client running and start gaming as usual.
• Paid challenges
  These challenges can be with a smaller or larger token entry. These challenges cost between 5-20 tokens to join and offer part of a prize money pool if you win. The size of the prize money depends on how big the entry is and where you place on the leaderboard. You need to actively join all paid challenges to be able to compete. Once you're signed up, just have the client running and start gaming as usual.