Every character has its own contract that is used to earn rewards at the end of sessions. Bounty Boxes, Royale Bounty Boxes, and Crowns are limited based on how many contracts your character has left.
Your character automatically gets a new contract over time. This contract will regenerate until it reaches the maximum amount of your character and determines how many valuable sessions reward you can get. Players can extend their sessions with different in-game rewards like Contract Books.