How do I claim this action quest?

This is my first time doing action quests, and I cleared stage 20 but can't claim the reward. I wonder if this is like a hidden bug and I need to contact support separately? Anyway, it takes about 30-40 minutes to clear stage 20. Setting aside the ads, the unnecessary screen effects make it frustrating. It's not particularly fun, and I have to figure out how to deal with new objects based on guesswork without any explanation. Also, if you don't watch ads, the rewards are scarce. I think I'll stop here.