:param payment_psp_object: an instance representing the original payment in the psp
        :param amount: the amount to refund
        :param client_ref: a reference that will appear on the customer's credit card statement
        :return: a tuple (success, refund_psp_object)

def refund_payment(self, payment_psp_object: Model, amount: Money, client_ref: str) -> Tuple[bool, Model]:
        """
        :param payment_psp_object: an instance representing the original payment in the psp
        :param amount: the amount to refund
        :param client_ref: a reference that will appear on the customer's credit card statement
        :return: a tuple (success, refund_psp_object)
        """
        pass