When you pay a BitPay invoice, your payment goes to a BitPay address. We pay network-based miner fees (just like you pay to send BTC or BCH) to move these funds so we can combine them for processing in something called a "UTXO sweep". The Network Cost is a fee charged to purchasers which helps to cover BitPay's miner fee cost for this UTXO sweep.
Miner fees are highly variable costs for BitPay based on network conditions, so the Network Cost fee also changes to reflect network conditions. Read our original post about why we introduced the Network Cost in February 2017.
This fee is used for BitPay's UTXO sweep, so it is not returned with refunds.
We strongly recommend that you send a miner fee with your bitcoin payment. Miner fees are given to the bitcoin miner (specialized hardware that processes transactions on the Bitcoin or Bitcoin Cash network) that appends the transaction to the Bitcoin or Bitcoin Cash blockchain. These miner fees are not BitPay fees, but they do increase the likelihood that your transaction will confirm on the Bitcoin or Bitcoin Cash network in less time.
A simple way to ensure that your transaction includes an appropriate fee is to adjust your bitcoin wallet settings to include a dynamically-calculated fee. Our bitcoin wallet BitPay includes this setting option, which will help ensure that your transaction confirms normally even at times of high network traffic.
Refund Miner Fee Cost
If you underpay or overpay an invoice and initiate a refund to yourself, BitPay will deduct the miner fee cost of returning the payment from the total refund amount you receive.
If you are a BitPay merchant and issue a full refund to your customers, the miner fee amount will be deducted from your merchant ledger balance. The deduction will be added as a separate entry in your BitPay ledger after the refund is executed.