Bex API uses Basic Authentication for authentication. This involves a username and a password in base64 sent in the header as Authorization.
var request = (HttpWebRequest)WebRequest.Create(url);
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(apiKey+":"+secret)
var base64EncodedToken = System.Convert.ToBase64String(plainTextBytes);
request.PreAuthenticate = true;
request.Headers.Add("Authorization", "Basic " + base64EncodedToken);
There can be many different api-versions up. Unless you have been informed of using a different api, we suggest using the default one i.e Bex API.
Setup an API-key in Bex and give it the proper settings.