Inquiry about Unreceived Hidden Quest Rewards

First, take a screenshot of your completed hidden quest. Then, click on your profile, tap the gear icon in the upper right corner, go to Customer Center > My Inquiries > Inquiry History, and tap 'Inquire' in the upper right. For the inquiry type, select 'Hidden Quest'. You'll then see a game selection, and after choosing the game, the hidden quests for that game will appear. Select 'Unrewarded Hidden Quest', upload your screenshot, and write your inquiry. Replies might be delayed during holidays or weekends, but don't worry, even if the hidden quest disappears after you inquire, the reward will still be processed (it seems you have 7 days to claim it).

Yes, thank you ^^