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API Post with parameters return 503 error

I sending requests to an API which was recently updated. All GET requests work perfectly but POST requests with parameters return a 503 error with about 20s timeout. POST requests without parameter work fine and POST requests using Postman work fine. It look to me like there is something with the request.ContentLength as each time I try to change the code to calculate the size the request fails immediately.
HttpWebRequest request = HttpWebRequest.Create("https://myAPIURL") as HttpWebRequest;
request.ContentType = "application/x-www-form-urlencoded";
request.Method = "POST";
request.Credentials = new NetworkCredential(APIUsername, APIPassword);
request.PreAuthenticate = true;
string param = "name=Test&description=MyDescription";
byte[] byteArray = Encoding.UTF8.GetBytes(param);
request.ContentLength = dataStream.Length;
try {
using (Stream stOut = request.GetRequestStream())
{
stOut.Write(byteArray, 0, byteArray.Length);
}
using (HttpWebResponse resp = request.GetResponse() as HttpWebResponse)
{
// Do some stuff
}
}
catch (WebException wex)
{
// catch error HTTP/1.1 503 Service Unavailable
}
The code is inspired from https://learn.microsoft.com/en-us/dotnet/framework/network-programming/how-to-send-data-using-the-webrequest-class
I have tried:
Removing the request.ContentLength
Copying the Postman contentlenght value which is slightly higher
Compare the Postman and my code request using Fiddler
Search for similar qestions such as curl with POST method working, but fetch API return error 503

How to pass parameter to Post URL C#

My code :
string postData = "'Country+Code':'US'&'Start+Date':'2018-01-01'&'End+Date':'2018-07-02'";
byte[] byteArray = Encoding.UTF8.GetBytes(postData);
request.ContentLength = byteArray.Length;
Stream dataStream = request.GetRequestStream();
dataStream.Write(byteArray, 0, byteArray.Length);
dataStream.Close();
request.Headers["Authorization"] = "Bearer " + accessToken;
var response = (HttpWebResponse)request.GetResponse();
I am getting 404 not found error :
I guess problem in Post data so i tride :
//string postData = "'Country Code':'US'&'Start Date':'2018-01-01'&'End Date':'2018-07-02'";
// string postData = "Country Code:'US':1&Start Date:'2018-01-01'&End Date:'2018-07-02'";
But still got error : 404 not found ,
finding correct way ?

If http status you receiving as 404 (Method Not Found), there are several possibilities for such error :
Ensure service hosted
Url Incorrect
If in case url correct then the ensure the service host as POST method. If its hosted as PUT & if you are calling it as POST then you may receive such error.
If all above case you have verified , cross verify whether you are sending the expected input data as per contract.

c# .net Http response 411 length required when length is included

I'm trying to get a simple response from a local .net site of my own. (Really I'm just trying to see what the content-body looks like from the server side.) Here is the controller method that's sending the response:
public HttpResponseMessage Post([FromBody]string value)
{
data.Add(value);
var msg = Request.CreateResponse(HttpStatusCode.Created);
msg.Headers.Location = new Uri(Request.RequestUri + "/" + (data.Count-1).ToString());
msg.Content = new StringContent(value);
return msg;
}
And here is the code that's making the request:
HttpWebRequest request;
request = (HttpWebRequest)WebRequest.Create ("http://localhost:50203/api/Values");
request.Method = "POST";
try
{
WebResponse response = (HttpWebResponse)request.GetResponse();
Stream dataStream = response.GetResponseStream();
byte[] requestBody = ASCIIEncoding.ASCII.GetBytes(HttpUtility.UrlEncode("grant_type=client_credentials"));
request.ContentLength = requestBody.Length;
dataStream.Write(requestBody, 0, requestBody.Length);
StreamReader reader = new StreamReader(dataStream);
myString = reader.ReadToEnd();
}
I'm getting the response message: HTTP Error 411. The request must be chunked or have a content length. But as you can see I DO assign the content length in the line: request.ContentLength = requestBody.Length;.
Why am I getting this error?

Thanks to help from itsme86 I was able to see what was happening. It had to do with misunderstanding the HttpWebRequest method. I was trying to set the content length and write to the request after I'd already posted it using the GetResponse method. I should have posted the length first. This wasn't a particularly good question, and no one else should answer.

REST API PATCH request

I'm trying to send requests and get responses from MailChimp API . . so far, GET, POST and DELETE are working good however, PATCH always results to Bad Request can you identify the error in this code?
string data = "{\"name\": \"TestListTWOTWOTWO\"}";
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(uri);
request.Headers[HttpRequestHeader.Authorization] = accessToken;
request.Method = "PATCH";
request.ContentType = "text/plain;charset=utf-8";
System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();
byte[] bytes = encoding.GetBytes(data);
request.ContentLength = bytes.Length;
using (Stream requestStream = request.GetRequestStream())
{
// Send the data.
requestStream.Write(bytes, 0, bytes.Length);
}
var response = (HttpWebResponse)request.GetResponse();
var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
the error occus on the line with request.GetResponse();
it is an unhandled WebException saying The remote server returned an error: (400) Bad Request
after checking the error response, here's the what it says
"Your request doesn't appear to be valid JSON:
\nParse error on line 1:\nPATCH /3.0/lists/9bb\n^\n
Expected one of: 'STRING', 'NUMBER', 'NULL', 'TRUE', 'FALSE', '{', '['"

Many C# libraries seem to try to use the Expect: 100-Continue header, which MailChimp/Akamai has a problem with when combined with PATCH. You have two options.
Turn off Expect: 100-Continue in your HTTP library. In one C# library, you do that with a line of code like Client.DefaultRequestHeaders.ExpectContinue = False
Tunnel the PATCH request through HTTP POST using the X-Http-Method-Override header. Here's more details on that header.

Cause PATCH is a quite new RFC, so you would not expect that more then a few services support it at all. You'd better check that if the service supports it.
You send request using json format, but set content type to "text/plain" is that OK?

c# HttpWebRequest and HttpWebResponse generic stuff

I am playing around with an app using HttpWebRequest to dialog with a web server.
I followed standard instructions I found on the web to build my request function that I tried to make as generic as possible (I try to get a unique method regardless of the method: PUT, POST, DELETE, REPORT, ...)
When I submit a "REPORT" request, I get two access logs on my server:
1) I get response 401 after following line is launched in debugger
reqStream.Write(Encoding.UTF8.GetBytes(body), 0, body.Length);
2) I get response 207 (multi-get, which is what I expect) after passing the line calling Request.GetResponse();
Actually, it seems to be the Request.GetRequestStream() line that is querying the server the first time, but the request is only committed once passing the reqStream.Write(...) line...
Same for PUT and DELETE, the Request.GetRequestStream() again generates a 401 access log on my server whereas the Request.GetResponse(); returns code 204.
I don't understand why for a unique request I have two server access logs, especially one that seems to be doing nothing as it always returns code 401... Could anybody explain what is going on? Is it a flaw in my code or a bad design due to my attempt to get a generic code for multiple methods?
Here is my full code:
public static HttpWebResponse getHttpWebRequest(string url, string usrname, string pwd, string method, string contentType,
string[] headers, string body) {
// Variables.
HttpWebRequest Request;
HttpWebResponse Response;
//
string strSrcURI = url.Trim();
string strBody = body.Trim();
try {
// Create the HttpWebRequest object.
Request = (HttpWebRequest)HttpWebRequest.Create(strSrcURI);
// Add the network credentials to the request.
Request.Credentials = new NetworkCredential(usrname.Trim(), pwd);
// Specify the method.
Request.Method = method.Trim();
// request headers
foreach (string s in headers) {
Request.Headers.Add(s);
}
// Set the content type header.
Request.ContentType = contentType.Trim();
// set the body of the request...
Request.ContentLength = body.Length;
using (Stream reqStream = Request.GetRequestStream()) {
// Write the string to the destination as a text file.
reqStream.Write(Encoding.UTF8.GetBytes(body), 0, body.Length);
reqStream.Close();
}
// Send the method request and get the response from the server.
Response = (HttpWebResponse)Request.GetResponse();
// return the response to be handled by calling method...
return Response;
}
catch (Exception e) {
throw new Exception("Web API error: " + e.Message, e);
}