public function changeReservation(
        $rno, $amount, $flags = KlarnaFlags::NEW_AMOUNT
    ) {
        $this->_checkRNO($rno);
        $this->_checkAmount($amount);
        $this->_checkInt($flags, 'flags');

        $digestSecret = self::digest(
            $this->colon($this->_eid, $rno, $amount, $this->_secret)
        );
        $paramList = array(
            $rno,
            $amount,
            $this->_eid,
            $digestSecret,
            $flags
        );

        self::printDebug('change_reservation', $paramList);

        $result = $this->xmlrpc_call('change_reservation', $paramList);

        return ($result  == 'ok') ? true : false;
    }