Fee deduction found in invoice

[Minako33]

When I create an invoice amount due is 3335.20 but I found after the invoice sent out there have a "fee deduction 148.75". why have such deduction?

[kernowlass]

@Minako33 

Your paypal fee???

How do you think paypal funds the service and pays their staff if you don't pay a fee to be able to receive instant payments from buyers (including from credit cards).