This fee is an estimate of what you need to pay if you want your Bitcoin transfer to be processed quickly. These funds go to miners, Cryptopay does not take anything for Bitcoin transactions.
At the moment the miner fee that we apply depends on how busy the network is at the moment. You can always see the applicable miner fee before you confirm the transaction.
However, we are planning to give our users an option to choose the sum they are willing to pay miners themselves.