Bonus Star Challenges are periodic offers to earn more Stars, and sometimes are personalized for you. For example, if you buy a lot of lattes, you may get a Buy 3 lattes before 11am within 4 days and earn 40 Stars. Challenges will be emailed (if you opted-in to receive marketing emails from Starbucks) or on the app. Expert tip: Make sure you activate or join each promotion, and follow the details of the offer, or you will not qualify for the extra Stars.