League of Legends is an online game and is played with a large number of players, the customisations that players are allowed to purchase do not affect the gameplay.
To make these purchases, players will have to use the in-game currency, RP or Riot Points. Riot Points can be used to purchase a plethora of items in the game.
Putting real-world money into a game is not a privilege that every player has, therefore, they can use the Microsoft Rewards system to earn some RP for League of Legends.