post How to send a POST webservice API?

[Nep]

I have a code that firstly read the cart rules and check if there is any duplicate code and this part works fine. I can get from the "GET" service.

However, when I move on to "POST", it keeps returning server status 200 to me. It seems it changed from POST to GET automatically. Is there any way to fix this?

I am also the admin to the prestashop. I have already created the webservice and enable the get and post function for the cart rules.
 

protected void CreateRecordPresta(string Coupon_Code, float Reduction_amount)
    {
        try
        {
            string PostURL = $"https://www.domain.com.xx/api/cart_rules&ws_key={WebService_LoginName}";
            HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(PostURL);
            webRequest.Credentials = new NetworkCredential(WebService_LoginName, WebService_Password);
            webRequest.Method = "POST";
            //webRequest.ContentType = "application/xml";
            webRequest.ContentType = "application/x-www-form-urlencoded;charset=utf-8";

            string CurrentDate = DateTime.Now.ToString("yyyy-MM-dd");
            string CurrentTime = DateTime.Now.ToString("HH:mm:ss");
            string Current = CurrentDate + " " + CurrentTime;
            string DateEnd = DateTime.Now.AddMonths(2).ToString("yyyy-MM-dd");
            string description = "";
            string Coupon_no = Coupon_Code;
            float reduction_amount = Reduction_amount;
            //int Customer_id = 4641;
            //Create POST data and convert it to a byte array.
            String PostData = "<?xml version='1.0' encoding='UTF-8'?>" +
                "<prestashop xmlns:xlink=\"http://www.w3.org/1999/xlink\">" +
                "<cart_rule>" +
                //$"<id_customer><![CDATA[{Customer_id}]]></id_customer>" +
                $"<date_from><![CDATA[{Current}]]></date_from>" +
                $"<date_to><![CDATA[{DateEnd} 00:00:00]]></date_to>" +
                $"<description><![CDATA[{description}]]></description>" +
                "<quantity><![CDATA[1]]></quantity>" +
                "<quantity_per_user><![CDATA[1]]></quantity_per_user>" +
                "<priority><![CDATA[1]]></priority>" +
                //"< partial_use >< ![CDATA[0]] ></ partial_use >" +
                $"<code><![CDATA[{Coupon_no}]]></code>" +
                //"< minimum_amount >< ![CDATA[0.00]] ></ minimum_amount >"+
                //"< minimum_amount_tax >< ![CDATA[0]] ></ minimum_amount_tax >" +
                "<minimum_amount_currency><![CDATA[1]]></minimum_amount_currency>" +
                //"< minimum_amount_shipping >< ![CDATA[0]] ></ minimum_amount_shipping >" +
                //"< country_restriction >< ![CDATA[0]] ></ country_restriction >" +
                //"< carrier_restriction >< ![CDATA[0]] ></ carrier_restriction >" +
                //"< group_restriction >< ![CDATA[0]] ></ group_restriction >" +
                "<cart_rule_restriction><![CDATA[1]]></cart_rule_restriction>" +
                "<product_restriction><![CDATA[1]]></product_restriction>" +
                //"< shop_restriction >< ![CDATA[0]] ></ shop_restriction >" +
                //"< free_shipping >< ![CDATA[0]] ></ free_shipping >" +
                //"< reduction_percent >< ![CDATA[0.00]] ></ reduction_percent >" +
                $"<reduction_amount><![CDATA[{reduction_amount}]]></reduction_amount>" +
                //"< reduction_tax >< ![CDATA[0]] ></ reduction_tax >" +
                ////"< reduction_currency >< ![CDATA[1]] ></ reduction_currency >" +
                //"< reduction_product >< ![CDATA[0]] ></ reduction_product >" +
                //"< reduction_exclude_special >< ![CDATA[0]] ></ reduction_exclude_special >" +
                //"< gift_product >< ![CDATA[0]] ></ gift_product >" +
                //"< gift_product_attribute >< ![CDATA[0]] ></ gift_product_attribute >" +
                //"< highlight >< ![CDATA[0]] ></ highlight >" +
                "<active><![CDATA[1]]></active>" +
                ////$"< date_add >< ![CDATA[{Current}]] ></ date_add >" +
                ////$"< date_upd >< ![CDATA[{Current}]] ></ date_upd >" +
                "<name>" +
                "<language id=\"1\" xlink:href=\"https://www.domain.com.xx/api/languages/1\">" +
                $"<![CDATA[Test]]>" +
                "</language>" +
                "<language id=\"2\" xlink:href=\"https://www.domain.com.xx/api/languages/2\">" +
                $"<![CDATA[Test]]>" +
                "</language>" +
                "</name>" +
                "</cart_rule>" +
                "</prestashop>";
            Byte[] byteArray = Encoding.UTF8.GetBytes(PostData);
            //Set the ContentType property of the WebRequest.
            //webRequest.ContentType = "application/x-www-form-urlencoded"
            //Set the ContentLength property of the WebRequest.
            webRequest.ContentLength = byteArray.Length;
            //Get the request stream.
            Stream stream = webRequest.GetRequestStream();
            //Write the data to the request stream
            stream.Write(byteArray, 0, byteArray.Length);
            //Close the Stream object
            stream.Close();

            //Get the response
            HttpWebResponse responsepost = (HttpWebResponse)webRequest.GetResponse();
            //Display the status.
            System.Diagnostics.Debug.WriteLine(responsepost.StatusCode.ToString());//StatusCode
            System.Diagnostics.Debug.WriteLine(responsepost.StatusDescription.ToString());
            //Console.WriteLine(CType(response, HttpWebResponse).StatusDescription)
            //Get the stream containing content returned by the server & Open the stream using a StreamReader for easy access.
            StreamReader reader = new StreamReader(responsepost.GetResponseStream());
            //Read the content.
            String responseFromServer = reader.ReadToEnd();
            //Display the content.
            System.Diagnostics.Debug.WriteLine(responseFromServer);
            //Clean up the streams.
            reader.Close();
            stream.Close();
            responsepost.Close();

            return;
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine("UnkownError");
            alert.Text = Resources.Resource.Redeem_Error;
            alert.Visible = true;
            CreateButton.Enabled = true;
            return;
        }
    }

It returns sth like this
 

<prestashop xmlns:xlink="http://www.w3.org/1999/xlink">
<cart_rules>
<cart_rule id="4" xlink:href="https://domain.com.xx/api/cart_rules/4"/>
<cart_rule id="12" xlink:href="https://domain.com.xx/api/cart_rules/12"/>
<cart_rule id="14" xlink:href="https://domain.com.xx/api/cart_rules/14"/>
<cart_rule id="15" xlink:href="https://domain.com.xx/api/cart_rules/15"/>
</cart_rules>
</prestashop>

Is there anythings that I need to modify?

Edited February 20, 2023 by Nep (see edit history)

[Nep]

I am also the admin to the presta shop. I have already created the webservice and enable the get and post function for the cart rules.