At this time you cannot bring your own payment processor with you. In all transactions we internally use Stripe for payment processing and act as the merchant. This means that when your clients pay, money first flows to us, and then we immediately send the payout to you. The payment processing fees you see advertised are inclusive of all fees and you do not pay any additional fees.
The reason we do this is because it gives us full control over the payment experience and lets us provide features that we otherwise could not. For example, we let you decide whether you want to pay payment processing fees or whether you want to pass them onto clients. This is only possible because of the setup we have in place.