def METHOD_NAME(reservation, reason=None):
    if not reservation.is_accepted:
        raise ValueError('Reservation is not confirmed')
    notification = ReservationNotification(reservation)
    return [_f for _f in [
        notification.compose_email_to_user(template_name='confirmation_email_to_user', reason=reason),
        notification.compose_email_to_manager(template_name='confirmation_email_to_manager', reason=reason),
    ] if _f]