Praise be to Allah.
PayPal is a commercial website which allows the user to transfer money through the Internet and email to various addresses. It also allows the user to send money that has been sent to him to other people or to transfer it to a bank account. This service is regarded as an alternative to traditional paper methods such as checks or money transfers.
PayPal enables payments to vendor websites, Internet auctions and so on, where there is an additional fee for the website. In October 2002, PayPal became a wholly owned subsidiary of eBay. The company’s headquarters are located in California, in the United States of America.
Holders of PayPal accounts must be above the age of eighteen years, and have a debit or credit card or a bank account. They must also have an email address.
End quote from Wikipedia.
There is nothing wrong with using this website and paying commission to it in return for offering these services, namely the transfer of money from the purchaser to the seller or anyone else. In fact the website does not receive commission from the purchaser; rather it receives it from the seller. The seller may add this cost to the price of the item, and there is nothing wrong with that, but the transaction must be done with an Islamically-acceptable credit card. See the answer to question no. 118034 .
And Allah knows best.