I am using following code.

string URL = "https://rms-world-check-one-api-pilot.thomsonreuters.com/api-gateway-service-rest/api/v1/groups";

System.Net.Http.HttpClient client = new System.Net.Http.HttpClient();
client.BaseAddress = new System.Uri(URL);
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("basic", authorisation); //Used from Postman Environment
client.DefaultRequestHeaders.Date = dToday; //Used from Postman Environment

System.Net.Http.HttpContent content = new StringContent("", UTF8Encoding.UTF8, "application/json"); //Since there are no parameters to send
HttpResponseMessage messge = client.PostAsync(URL, content).Result;

But I am always getting 401 Unauthorized error. I also tried creating "authorisation" string in .NET by using .NET HMAC libraries, still no luck.

Any help will be appreciated much.