Merge Dragons levels..

What qualifies as beating a level in Merge Dragons? The offer instructions aren't exactly clear as to what exactly you're supposed to do here. I know it means to do the quests, but how exactly? Are we supposed to get 3 stars on each level? Are we supposed to finish 3 levels of a challenge? I got past level 21 and didn't see a pending credit, even though they credited me for Dragon Powers and making a purchase.