Every time you get promoted to a new Level, you’ll get a one-time bonus, with an attached wagering requirement, that you can use to play slots, wager them, and withdraw your wins!
7.1.2 If you’ve collected your bonus once, downgraded to a lower Level, and then returned to the same higher Level, you won’t be able to claim the bonus again.
7.1.3 The bonus amount will be based on the new Level you joined and will be credited only once when you reach a certain Level for the first time!
More details about the Reward Program can be seen here.