All perfect praise be to Allah. Blessings and peace be upon Prophet Mohammad.
After navigating through “Paypal,” it was clear that it is an advanced website that contains systems of payment, withdrawal and electronic money transfer, and that it is a traditional banking site that deals in usury. However, there is no harm in raising donations through it for a legitimate cause because Sharia doesn`t forbid dealing with a usurious party in non-usurious transactions, provided that the transaction meets the conditions of Sharia, and doesn’t help in committing what is unlawful.
It was stated in the complement of the book [Al-Majmou`”(13/178)]: “ It is permissible to conclude a transaction with one whose money is lawful and unlawful if he couldn`t tell which is which because the Prophet (PBUH) used to deal with the Jews who considered the price of the wine as lawful and dealt in usury.”
However, it is better and more pious for a Muslim to abandon such a transaction. Moreover, there is no harm that the one donated for transfers the donations through the same website in case it was going to charge an amount known to both parties in return for the transfer service. And Allah knows best.