Traccar API 500 Error on getting positions

Please tell me is this a valid http request from getting past positions

http://track.gatsan.com:80/api/positions?from=2018-03-18T18:30:00Z&to=2018-03-20T18:30:00Z

That's a URL, not a request. And even the URL is not correct. There is no device or group.

Please add time request to this code. That would be really helpful

private void test()
        {
            string url = "http://track.gatsan.com:80/api/positions";

            var pairs = new List<KeyValuePair<string, string>> { };

            
            var byteArray = Encoding.ASCII.GetBytes("admin" + ":" + "admin");

            var client = new HttpClient();
            client.DefaultRequestHeaders.TryAddWithoutValidation("Content-Type", "application/json");
            client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            
            var content = new FormUrlEncodedContent(pairs);

            var response = client.GetAsync(url).Result;
            HttpStatusCode statusCode = response.StatusCode;

            switch (statusCode)
            {
                case HttpStatusCode.OK:
                    {
                        response.EnsureSuccessStatusCode();
                        string res = response.Content.ReadAsStringAsync().Result;
                        if (response.IsSuccessStatusCode)
                        {
                            JArray rows = JArray.Parse(res);
                            if (rows.HasValues)
                            {
                                foreach (JToken row in rows)
                                {
                                    MessageBox.Show(row.ToString());
                                }
                            }
                        }
                    }
                    break;
            }

        }