Got a hidden reward, but no proof pic.

I also cleared Stage 20. It's 40k gems. But the hint for the Stage 20 clear mission said: 'Complete the mission within 3 days after clearing Stage 15.'... Looks like there was a Stage 15 too. *My Stage 12 clear had an error and it still hasn't been fixed, so I'm waiting. I know how to contact customer service, so you don't need to tell me^^ㅎ I'm not contacting them because it's the weekend~🤭