How to react to card network on onpaymentmethodselected?

We're currently evaluating Apple Pay as a payment method on our site. For Amex US credit card payments, we charge a payment fee. For other credit cards, there is no such fee.

However, for Apple Pay it seems we cannot configure this. What we currently tried is to implement onpaymentmethodselected. However, only the card type is part of the event, not the card network.

Example code:

session.onpaymentmethodselected = event => {

   /* event.paymentMethod only contains {type: "credit"} */
   console.log('onpaymentmethodselected', event.paymentMethod);

   /* event.paymentMethod.network is therefore undefined, if we could have here 'amex', 'mastercard' etc, we could implement the payment fee we currently have*/
   console.log('onpaymentmethodselected', event.paymentMethod.network);

   session.completePaymentMethodSelection({});
};

Is there a way to access the network in this callback?

Or is there another way to implement payment fees with certain networks used via Apple Pay?