var url = "http://domain.herokuapp.com/api/createuser";
var item = new { username = "kasunrt1", email = "dgggdgdg@test.com", password = "3333", tele = "123456789" };
var uri = new Uri(url);
var json = JsonConvert.SerializeObject(item);
var content = new StringContent(json, Encoding.UTF8, "application/json");
var client = new HttpClient();
var result = await client.PostAsync(url, content);

var result = await client.PostAsync("http://domain.herokuapp.com/api/createuser/nameTest/testmail@gmail.com/346gf4/123456789", null);