curl Request with ASP.NET

The default HTTP method for WebRequest is GET. Try setting it to POST, as that's what the API is expecting

myReq.Method = "POST";

I assume you are posting something. As a test, I'm going to post the same data from their curl example.

string url = "https://YOUR_COMPANY_HERE.beebole-apps.com/api";
string data = "{\"service\":\"absence.list\", \"company_id\":3}";

WebRequest myReq = WebRequest.Create(url);
myReq.Method = "POST";
myReq.ContentLength = data.Length;
myReq.ContentType = "application/json; charset=UTF-8";

string usernamePassword = "YOUR API TOKEN HERE" + ":" + "x";

UTF8Encoding enc = new UTF8Encoding();

myReq.Headers.Add("Authorization", "Basic " + Convert.ToBase64String(enc.GetBytes(usernamePassword)));


using (Stream ds = myReq.GetRequestStream())
{
ds.Write(enc.GetBytes(data), 0, data.Length); 
}


WebResponse wr = myReq.GetResponse();
Stream receiveStream = wr.GetResponseStream();
StreamReader reader = new StreamReader(receiveStream, Encoding.UTF8);
string content = reader.ReadToEnd();
Response.Write(content);