It's impossible to answer. The message says it was PayPal that canceled the payment, not Itch, and you're asking the Itch community, which also doesn't have access to any additional information.

The little I know is that PayPal has certain risk criteria. If it thinks a transaction is fraudulent, it cancels it. But it's best to check with PayPal directly for the exact reasons.

From what I've read, that risk factor is usually the amount or the country. For example, if your account normally has deposits of $100 and suddenly, you receive $10,000, that raises suspicions.