Order::getTotalPrice PHP Method

    public function getTotalPrice()
    {
        return (double) $this->total_price - (double) $this->discount - (double) $this->coupon_discount;
    }

 public function renderCheckoutForm(Payment $payment, Order $order, $return = false)
 {
     $settings = $payment->getPaymentSystemSettings();
     $mrhLogin = $settings['login'];
     $mrhPass1 = $settings['password1'];
     $culture = $settings['language'];
     $invId = $order->id;
     $invDesc = Yii::t('RobokassaModule.robokassa', 'Payment order #{id} on "{site}" website', ['{id}' => $order->id, '{site}' => Yii::app()->getModule('yupe')->siteName]);
     $outSum = Yii::app()->money->convert($order->getTotalPrice(), $payment->currency_id);
     $crc = md5("{$mrhLogin}:{$outSum}:{$invId}:{$mrhPass1}");
     $form = CHtml::form($settings['testmode'] ? "http://test.robokassa.ru/Index.aspx" : "https://merchant.roboxchange.com/Index.aspx");
     $form .= CHtml::hiddenField('MrchLogin', $mrhLogin);
     $form .= CHtml::hiddenField('OutSum', $outSum);
     $form .= CHtml::hiddenField('InvId', $invId);
     $form .= CHtml::hiddenField('Desc', $invDesc);
     $form .= CHtml::hiddenField('SignatureValue', $crc);
     $form .= CHtml::hiddenField('Culture', $culture);
     $form .= CHtml::submitButton(Yii::t('RobokassaModule.robokassa', 'Pay'));
     $form .= CHtml::endForm();
     if ($return) {
         return $form;
     } else {
         echo $form;
     }
 }