Depending on the Active Bonus in your account, there are some instances where you may have to play your pending winnings on specific eligible games. These games will be noted in the Terms and Conditions of the given promotion, as well as the My Bonuses page.
You can see important information regarding your Active Bonuses by going to My Bonuses and selecting the promotion you are looking for.
Here you can find information on Expiration Dates, Eligible Games, Wagering Requirement Progression, Terms and Conditions, etc.