when calling the API from postman will execute without any problem but when calling it from C# code

I get the error "'The remote server returned an error: (401) Unauthorized.'"

string gatewayurl = "/v2/";

string gatewayhost = "rms-world-check-one-api-pilot.thomsonreuters.com";

// Here is where you enter your api keys

string requestendpoint = "https://rms-world-check-one-api-pilot.thomsonreuters.com/v2/cases/"+ caseid + "/screeningRequest";

// Assemble the POST request - NOTE every character including spaces have to be EXACT

// for the API server to decode the authorization signature

string dataToSign = "(request-target): post " + gatewayurl + "cases/" + caseid + "/screeningRequest\n" +

"host: " + gatewayhost + "\n" + // no https only the host name

"date: " + date; // GMT date as a string

Console.WriteLine("---api secret---");

Console.WriteLine(apisecret);

Console.WriteLine("---dataToSign---");

Console.WriteLine(dataToSign);

Console.WriteLine("string hmac = generateAuthHeader(dataToSign, apisecret);");

// The Request and API secret are now combined and encrypted

string hmac = generateAuthHeader(dataToSign, apisecret);

// Assemble the authorization string - This needs to match the dataToSign elements

// i.e. requires host date content-type content-length

//- NOTE every character including spaces have to be EXACT else decryption will fail with 401 Unauthorized

string authorisation = "Signature keyId=\"" + apikey + "\",algorithm=\"hmac-sha256\",headers=\"(request-target) host date content-type content-length\",signature=\"" + hmac + "\"";

Console.WriteLine("---Hmac---");

Console.WriteLine(hmac);

//Console.WriteLine(authorisation);

// Send the Request to the API server

HttpWebRequest WebReq = (HttpWebRequest)WebRequest.Create(requestendpoint);

// Set the Headers

WebReq.Method = "POST";

WebReq.Headers.Add("Authorization", authorisation);

WebReq.Headers.Add("Cache-Control", "no-cache");

// WebReq.ContentLength = msg.Length;

WebReq.Date = dateValue; // use datetime value GMT time

// Set the content type of the data being posted.

// WebReq.ContentType = "application/json";

// WebReq.ContentLength = byte1.Length;

Stream newStream = WebReq.GetRequestStream();

// newStream.Write(byte1, 0, byte1.Length);

// Get the Response - Status OK

HttpWebResponse WebResp = (HttpWebResponse)WebReq.GetResponse();