Question about national park permits

I have run into a complication in applying for park permits. My application for Snow Mountain was confirmed, which is great. Now I am trying to apply for wuling sixiu for a different date, but it says I cannot apply because I already applied for the park using my passport number. What’s the deal? Why wouldn’t I be able to apply for a park more than once?

I’m wondering if I need to cancel my first application (I was already approved and I have the physical copy), and reapply. Or is there another way?