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C# HTTP request 401 and 500 error

I've been working on the Walmart API but I keep getting either the 401 error or the 500 error when I run the code
public void post()
{
byte[] data = Encoding.ASCII.GetBytes(
$"username={user}&password={password}");
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://marketplace.walmartapis.com/v2/feeds?feedType=item");
request.Method = "POST";
request.Accept = "application/xml;";
request.ContentLength = data.Length;
request.Headers.Add("WM_SVC.NAME", "Walmart Marketplace");
request.Headers.Add(authId);
request.Headers.Add("WM_CONSUMER.ID", user);
request.Headers.Add( time);
request.Headers.Add(CorId);
using (Stream stream = request.GetRequestStream ())
{
stream.Write(data , 0, data.Length);
}
string responseContent = null;
using (WebResponse response = request.GetResponse())
{
using (Stream stream = response.GetResponseStream())
{
using (StreamReader sr99 = new StreamReader(stream))
{
responseContent = sr99.ReadToEnd();
}
}
}
MessageBox.Show(responseContent);
}
where authID is a signature generated from a jar file provided by walmart
time is also generated from the jar file
CorID is a randomly generated number
and user is the user id.
here is the link that describes the header parameters. Did I miss something in my header?
https://developer.walmartapis.com/#getting-started

There are multiple problems with your request. First, you are submitting a feed, but sending it as an application/xml when it should be a multipart/form-data request. Beyond this, your headers aren't set up properly and there is currently a major problem with submitting multipart/form-data requests to Walmart using C#. I have not seen a post from anyone successfully sending a feed to Walmart via C#. I am currently using C# to execute a batch file that then fires a modified version of the Walmart Java SDK which is capable of sending the multipart/form-data requests.
The reponse below is for any request other than feeds. I would start with the example listed below to get familiar with how you need to set your headers up. This is going to work for the majority of Walmart interfacing, but if the request is a feed style request, you will either need to come up with a better solution to the multipart/form-data issue, use the Java SDK, or wait for the C# SDK. If someone reads this and has a better answer as to how to submit feeds via C# exclusively I would love to hear about it!
Here is an example of an application/xml request that works.
string timestamp = CurrentTimeMillis().ToString().Trim();
string query = #"orders/"+poID+"/acknowledge";
string request = v3BaseUrl + query; //Constructed URI
string stringToSign = consumerId + "\n" +
request.Trim() + "\n" +
"POST" + "\n" +
timestamp + "\n";
string signedString = signData(stringToSign); //Your signed string
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(request);
webRequest.Accept = "application/xml";
webRequest.ContentType = "application/xml";
webRequest.Method = "POST";
webRequest.Headers.Add("WM_SVC.NAME", "Walmart Marketplace");
webRequest.Headers.Add("WM_SEC.AUTH_SIGNATURE", signedString);
webRequest.Headers.Add("WM_CONSUMER.ID", consumerId);
webRequest.Headers.Add("WM_SEC.TIMESTAMP", timestamp.ToString().Trim());
webRequest.Headers.Add("WM_QOS.CORRELATION_ID", Guid.NewGuid().ToString());
webRequest.Headers.Add("WM_CONSUMER.CHANNEL.TYPE", channelType);
webRequest.ContentLength = 0;
webRequest.Timeout = Timeout.Infinite;
webRequest.KeepAlive = true;
using (HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse())
{
if (response.StatusCode == HttpStatusCode.OK)
{
success = true;
}
}

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.

PayPal Pay Operation - error 81002

I'm not sure why this PayPal Pay operation is giving me this error even though I seem to have covered all the required fields:
Error Code: 81002 Severity: Error Message: Unspecified Method (Method Specified is not Supported)"
string postData = JsonConvert.SerializeObject(request);
value of postData:
"actionType=PAY
&currencyCode=USD
&cancelUrl=https%3a%2f%2fexample.com%2fcancel
&returnUrl=https%3a%2f%2fexample.com%2freturn
&requestenvelope.errorLanguage=en_US
&receiverList.receiver(0).email=recipientemail%40gmail.com
&receiverList.receiver(0).amount=0.05
&VERSION=94.0
&USER=bizemail-facilitator_api1.gmail.com
&PWD=xxxxx
&SIGNATURE=xxxxxxxxx"
Here's how I do the post:
SendRequest("https://api-3t.sandbox.paypal.com/nvp", postData);
public string SendRequest(string url, string postData)
{
var uri = new Uri(url);
var request = WebRequest.Create(uri);
var encoding = new UTF8Encoding();
var requestData = encoding.GetBytes(postData);
request.ContentType = "application/x-www-form-urlencoded";
request.Method = "POST";
request.Timeout = (300*1000); //TODO: Move timeout to config
request.ContentLength = requestData.Length;
using (var stream = request.GetRequestStream()) {
stream.Write(requestData, 0, requestData.Length);
}
var response = request.GetResponse();
string result;
using (var reader = new StreamReader(response.GetResponseStream(), Encoding.ASCII)) {
result = reader.ReadToEnd();
}
return result;
}

The method PAY doesn't exist on the NVP api. Full list of methods supported by that API is found here.
The PAY method, however, is defined in the Adaptive Payments API. Depending on your needs, you have two options:
Change the endpoint to https://svcs.paypal.com/AdaptivePayments/PAY and modify your values
Use another method, like DoDirectPayment, but I'm not sure it does what you want to.

I assume the value of postData is before you serialize it to a JSON string, instead of after as you say, since it is clearly not a JSON string.
If so, then it is already x-www-form-urlencoded, and you do not need to serialize it to a JSON string at all.
Or if you do after all, then change just this: request.ContentType = "application/json";

WebRequest POST form containing XML?

I am trying to use .Net WebRequest to POST a form. The form contains fields that are XML. (Among other things) I have tried the following code:
WebRequest req = WebRequest.Create(ctx.SvcUrl);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
using (var writer = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII))
{
string reqBody = "first=<bill/>&last=smith"; //(embedded <>) - 500 Internal Server Error
writer.Write(reqBody);
}
rsp = req.GetResponse();
var strm = rsp.GetResponseStream();
var rdr = new StreamReader(strm);
string input = rdr.ReadToEnd();
The <> in reqBody causes a 500 - Internal Server error.
What's the right way to encode this? Or are multi-part forms the answer??

Try using:
string reqBody = string.Format("first={0}&last={1}", HttpUtility.HtmlEncode("<bill/>"), "smith");

You need to encode the request. Use the HttpEncoder class.
using System.Web.Util;
WebRequest req = WebRequest.Create(ctx.SvcUrl);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
using (var writer = new StreamWriter(req.GetRequestStream(),
System.Text.Encoding.ASCII))
{
var encoder = new HttpEncoder();
string reqBody = String.Format("first={0}&last={1}",
encoder.HtmlEncode("<bill/>"),
encoder.HtmlEncode("smith") );
writer.Write(reqBody);
}
rsp = req.GetResponse();
var strm = rsp.GetResponseStream();
var rdr = new StreamReader(strm);
string input = rdr.ReadToEnd();
I used String.Format() because I thought it looked nicer and made it clearer what I was doing, but it isn't necessary. You can build the string through string concatenation, too, as long as you pass it through HttpEncoder.HtmlEncode() first.

It turns out that UrlEncoding is being done automatically, so doing it myself can cause trouble. Also, the server I was connecting to couldn't handle any encoding. This muddied the water and made it difficult to see what was failing.
Bottom line solution was to get the server fixed to handle UrlEncoding.
As 'cheong00 on Microsoft's Forums' points out, to avoid the automatic, use TcpClient. But the encoding should be there.

C# WebRequest won't work with this link from LinkShare

This is driving me a bit nuts. I am trying to do something quite simple, and I have done it many times before. Just trying to call a REST API.
I am trying to call GetMessage with endpoint = "http://feed.linksynergy.com/productsearch?token=717f8c8511725ea26fd5c3651f32ab187d8db9f4b208be781c292585400e682d&keyword=DVD", and it keeps returning empty string. If I pass it any other valid URL, it will work. But if I just copy and paste the original URL into the web browser, it returns fine!
Can any smart developer tell me what's going on?
Code below. Thanks in advance.
James
public string GetMessage(string endPoint)
{
HttpWebRequest request = CreateWebRequest(endPoint);
using (var response = (HttpWebResponse)request.GetResponse())
{
var responseValue = string.Empty;
if (response.StatusCode != HttpStatusCode.OK)
{
string message = String.Format("POST failed. Received HTTP {0}", response.StatusCode);
throw new ApplicationException(message);
}
// grab the response
using (var responseStream = response.GetResponseStream())
{
using (var reader = new StreamReader(responseStream))
{
responseValue = reader.ReadToEnd();
}
}
return responseValue;
}
}
private HttpWebRequest CreateWebRequest(string endPoint)
{
var request = (HttpWebRequest)WebRequest.Create(endPoint);
request.Method = "GET";
request.ContentLength = 0;
request.ContentType = "text/xml";
return request;
}

Not sure why your setting ContentLength/ContentType - that is generally for HTTP POST, where there is a request body for which you write data to via a stream.
This is a HTTP GET, so there is no request body. (just URI w/ query string)
This should work:
using System;
using System.IO;
using System.Net;
using System.Text;
// Create the web request
HttpWebRequest request = WebRequest.Create("http://www.someapi.com/") as HttpWebRequest;
// Get response
using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
{
// Get the response stream
StreamReader reader = new StreamReader(response.GetResponseStream());
// Console application output
Console.WriteLine(reader.ReadToEnd());
}
EDIT
#Gabe is also quite right - try this on another computer, that is isn't behind any kind of firewall/proxy server.
My work PC was behind a proxy server, so in order to make REST-based HTTP calls, i needed to do this:
var proxyObject = new System.Net.WebProxy("http://myDomain:8080/", true);
System.Net.WebRequest req = System.Net.WebRequest.Create("http://www.someapi.com/");
req.Proxy = proxyObject;
proxyObject.Credentials = New System.Net.NetworkCredential("domain\username","password")