HttpWebRequest Error - The underlying connection was closed: An unexpected error occurred on a send.

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C#

C#3.5

REST

HTTP

webservice

, +

Hi, I get always that error "The underlying connection was closed: An unexpected error occurred on a send" when I try to invoke the REST service by GET method. (The service Respond in JSON Format)

this is my code:

string uri = "https://vvzerlgggk.execute-api.us-east-1.amazonaws.com/dev/api/efecty/payment/a1b2c3d4c5f6";
            
System.Net.ServicePointManager.ServerCertificateValidationCallback = ((sender, certificate, chain, sslPolicyErrors) => true);

HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(uri);

webRequest.KeepAlive = false;
webRequest.Method = "GET";
string hmac = "rDQ2ExmsC88zcpbT7nLu864U0hvOVx974FFfqqzP"; 
webRequest.Headers.Add("x-api-keys", hmac);
//webRequest.Timeout = 60 * 1000;

HttpWebResponse response;
            
try
{
     response = (HttpWebResponse)webRequest.GetResponse();
     StreamReader reader = new StreamReader(response.GetResponseStream());
     string body = reader.ReadToEnd();
}

catch (WebException wex)
{
     response = (HttpWebResponse)wex.Response;     
} 

What do you think could I improve?

Thanks