Alipay error Prestashop

	/**
     * @getProductCode
     */
    public function getProductCode()
    {
        return $this->product_code;
    }
   
    /**
     * @setProductCode
     */
    public function setProductCode($product_code)
    {
        $this->product_code = $product_code;
        $this->param_list['product_code'] = $product_code;
    }

public function hookPayment($params)
    {
        include_once(_PS_MODULE_DIR_.'alipay/api/loader.php');

        $currency_id = $params['cart']->id_currency;
        $currency = new Currency((int)$currency_id);
        $cart = new Cart($params['cart']->id);
        if (!ValidateCore::isLoadedObject($cart)) {
            return false;
        }
        if (in_array($currency->iso_code, $this->limited_currencies) == false) {
            return false;
        }
        $service = Configuration::get('ALIPAY_SERVICE_PAYMENT');
        $credentials = AlipayTools::getCredentials($service, false);

        $alipayapi = new AlipayApi($credentials);
        $alipayapi->setReturnUrl($this->getReturnUrl($cart->secure_key, $cart->id));
        $alipayapi->setNotifyUrl($this->getNotifyUrl($cart->secure_key, $cart->id));
        $alipayapi->setCharset('UTF-8');
        date_default_timezone_set('Asia/Hong_Kong');
        $payment_request = new PaymentRequest();
        $payment_request->setCurrency($currency->iso_code);
        $payment_request->setPartnerTransactionId(date('YmdHis').$cart->id);
        $payment_request->setGoodsDescription($this->getGoodsDescription());
        $payment_request->setGoodsName($this->getGoodsName($cart->id));
        $payment_request->setOrderGmtCreate(date('Y-m-d H:i:s'));
        $payment_request->setOrderValidTime(21600);
        $payment_request->setTotalFee($cart->getOrderTotal());
        $payment_request->setProductCode('NEW_OVERSEAS_SELLER');
        $alipayapi->prepareRequest($payment_request);
        $url = $alipayapi->createUrl();
        $this->smarty->assign(
            array(
                'module_dir' => $this->_path,
                'alipay_payment_url' => $url
            )
        );

        return $this->display(__FILE__, 'views/templates/hook/payment.tpl');
    }