What is the ruling on using PayPal, which combines a percentage and a fixed fee (4.4% + $0.3) for its transfer service, considering that it is almost indispensable at present? And is it permissible to use it for receiving and sending money?

It is permissible to transfer money for a known fee. The majority of jurists stipulate that the fee must be known and fixed, not a percentage, while the Hanbalis permitted the fee to be a percentage. As for combining a fixed fee with a percentage, its permissibility is narrated from Imam Ahmad and some of the early Muslims (Salaf). Some jurists, such as Sheikh Ibn Uthaymeen, have permitted this to ensure that workers do not tamper and to encourage productivity. Therefore, there is no objection for PayPal to take a fixed amount in addition to a percentage of the transferred amount for the transfer service.