A similar question has been asked here about transferring funds through PayPal but the purpose in this question is different: it is about buying something (or paying for something you are going to get in future) and not about pure funds transfer from one account to another.
There are two main ways to send money through PayPal:
- Sending money to friends and family - without paying any fees on any side
- Sending money to pay for goods and services - only the seller pays a fee: 3.4% + fixed fee (percentage and the fixed fee vary from country to country); the use of this kind of transaction is when you are sending money to a seller you don't know and you are not sure if the seller will actually ship you the item you agreed upon (could be over eBay, Facebook marketplace, or any other kind of market, as far as I know). If the seller doesn't ship you the item, or the item is does not match the agreed description then you have right to make a claim on PayPal and PayPal is going to refund you (whereas with the first option (Sending money to friends and family) this is not possible).
Is the way number 2 of sending money through PayPal permissible in Islam? To me this seems to be somewhere between a pure funds transfer and some kind of insurance, but this is only my uneducated guess.
Would the ruling change if we were in the role of the seller? Being the seller means you are the one who pays the fee.
Useful links:
https://www.paypal.com/us/brc/article/customer-disputes-claims-chargebacks-bank-reversals
https://www.paypal.com/an/smarthelp/article/What-are-the-fees-for-PayPal-accounts-FAQ690
https://www.paypal.com/uk/webapps/mpp/merchant-fees
https://www.paypal.com/uk/webapps/mpp/paypal-fees