Request throwing An existing connection was forcibly closed by the remote host only on C# request
<p>I'm having a hard time trying to consume a REST service from Cielo (credit/debit card gateway company). If I use postman it works:</p>

<pre><code>POST /1/sales/ HTTP/1.1
Host: apisandbox.cieloecommerce.cielo.com.br
MerchantKey: my_key
Content-Type: application/json
MerchantId: merc_id
Cache-Control: no-cache
Postman-Token: 6643cc5a-173a-f5db-8924-85ea8b7bbb55

{"MerchantId":"00000000-0000-0000-0000-000000000000","MerchantKey":null,"RequestId":"00000000-0000-0000-0000-000000000000","MerchantOrderId":"1223","Customer":{"Name":"Emerson Fitchy"},"Payment":{"PaymentId":"00000000-0000-0000-0000-000000000000","Type":"CreditCard","Amount":15700,"Installments":1,"Provider":null,"ProofOfSale":null,"Tid":null,"AuthorizationCode":null,"SoftDescriptor":null,"ECI":null,"Status":0,"ReturnCode":null,"ReturnMessage":null,"CreditCard":{"CardNumber":"0000000000000001","Holder":"Emerson Fitchy Santis","ExpirationDate":"12/2022","SecurityCode":"154","Brand":"Visa"}}}
</code></pre>

<p>And this is the C# code (at the moment, I tried also with <code>RestSharp</code> and <code>HttpClient</code> with the same results):</p>

<pre><code>var webrequest = (HttpWebRequest)WebRequest.Create(Constants.Cielo.GetSalesUrl());

webrequest.ContentType = "application/json";
webrequest.Method = "POST";
webrequest.Headers.Add("MerchantId", Constants.Cielo.Sandbox.MerchantId.ToString());
webrequest.Headers.Add("MerchantKey", Constants.Cielo.Sandbox.MerchantKey);

using (var streamWriter = new StreamWriter(webrequest.GetRequestStream()))
{
    var json = JsonConvert.SerializeObject(sale);
    streamWriter.Write(json);
}

var httpResponse = (HttpWebResponse)webrequest.GetResponse();
using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
    var result = streamReader.ReadToEnd();
    var x = result;
}
</code></pre>

<p>Any ideas on what am I doing wrong? I tried using Fiddler 4 but it's not picking up this request (I don't know why) and WireShark picks it up, but doesn't show the information the way Fiddler does (Maybe it's because I'm using https?).</p>

<p>Any ideas? </p>

<p>Thanks!</p>

<p><strong>EDIT</strong></p>

<blockquote>
  <p>Response/Exception</p>
</blockquote>

<p><a href="https://i.stack.imgur.com/pzi6j.png" rel="nofollow"><img src="https://i.stack.imgur.com/pzi6j.png" alt="enter image description here"></a></p>