Yes, they have specific packages where you can use your credits with which you are eligible for discount. sometimes trips are free you just need to pay for your flights but sometimes you need to extra but discounted amount. It totally depends on packages and what offer they have currently. Offers keeps changing after particular time.
Hope this helps
Sometimes its totally free which you will find very rare and sometimes you have to pay a discounted price. Please check always the exclusion lists. That's more important. Most of the time you have to bear your own flight charges.