You need 501 karma for downvoting, that exact number is undocumented on the FAQ page.
https://github.com/minimaxir/hacker-news-undocumented/blob/m...
For anyone else that curious about undocumented stuff, here are some previous discussions with that github link.
https://news.ycombinator.com/item?id=16437973 (Feb 2018)
https://news.ycombinator.com/item?id=19212822 (Feb 2019)
https://news.ycombinator.com/item?id=20292361 (June 2019)
https://news.ycombinator.com/item?id=23439437 (June 2020)