The service fee on a purchase covers the blockchain network costs of moving your payment to the merchant.
Where the cost comes from
After your payment arrives, the funds move several times inside our infrastructure before they reach the merchant. Each of those movements is a blockchain transaction, and every blockchain transaction carries a network fee paid to miners or validators. That fee is not fixed — it rises when the network is busy and falls when it is quiet.
Why it is charged to the buyer
The fee reflects the cost of the network you chose to pay on, so it is applied at the point where that choice is made. Networks differ considerably in cost, which is why the same purchase can carry a different fee depending on the cryptocurrency and network you select.
Seeing it before you pay
The amount shown on the checkout page is the total to send. There is nothing added afterwards — if you send exactly what the page shows, your order will be covered in full.