http://ciisqbg4cilbtc46tlqwkqxvzuf2ctgryzpunfsyjjk3s37g6zcyhoad.onion/refund
Be sure to include the payment processor used (PayPal, CCBill, BitPay, NOWPayments, XMR/Monero), the email address associated with the order, and the invoice/transaction ID. For obvious reasons, the number of refunds will be limited per customer.