Moments have at least one Reward Level, with some having up to a maximum of three, which will offer one to three FUT Stars respectively. You can start at the lowest Reward Level and work your way up, earning a FUT Star each Reward Level you complete, or you can try your hand at the highest Reward Level first to try to earn all unearned FUT Stars for that Moment in one go.
Different Reward Levels can change elements such as the Squad Requirements, time to complete, or CPU AI Difficulty as you increase/decrease the Reward Level.