What country are you from (or more directly, what country are your banks located in)? Also keep in mind that even before the insanity of the past couple months, Paypal was always a bit random at times.
Pardon, didn't see your earlier post. A heads up: if you want my attention when posting in a thread, be sure you're replying to me, rather than the original poster, or I may not see it. So:
"This is my first time buying a game on Itchio and from Taiwan."
Notably, this does not include TWD. Paypal is no longer processing your currency on Steam (from what I can tell), and presumably that has been expanded to Itch as well (possibly other gaming sites). I have no way of knowing why, aside from observing that it has happened in synch with the recent censorship push. Why TWD (and many others) and not major ones like USD and JPY? No idea.
That said, you can certainly try to join the subscribestar (https://subscribestar.adult/bitshift) for a single month (same price) and message me there once you have so I can toss you a game key. No idea whether Substar will play ball with your bank/card either though.