class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("*** START ***");
            Console.WriteLine("");

            GetPersonen();

            Console.WriteLine("");
            Console.WriteLine("*** END ***");
            Console.ReadLine();
        }

        private const string URL = "https://api.personio.de/v1/company/employees?limit=300&offset=0";
        private static string client_id = "xxxx";
        private static string client_secret = "xxxxxxxx";

        public static async void GetPersonen()
        {
            using (var client = new HttpClient())
            {
                client.BaseAddress = new Uri(URL);
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                client.DefaultRequestHeaders.Add("client_id", client_id);
                client.DefaultRequestHeaders.Add("client_secret", client_secret);

                var responseTask = client.GetAsync("employees");
                responseTask.Wait();

                var result = responseTask.Result;
                if (result.IsSuccessStatusCode)
                {

                    var readTask = result.Content.ReadAsAsync<Person[]>();
                    readTask.Wait();

                    var personen = readTask.Result;

                    foreach (var person in personen)
                    {
                        Console.WriteLine(person.Nachname);
                    }
                }
                else
                {
                    Console.WriteLine("{0} ({1})", (int)result.StatusCode, result.ReasonPhrase);
                }
            }
        }
    }

    public class Person
    {
        public string Vorname
        {
            get;
            set;
        }

        public string Nachname
        {
            get;
            set;
        }
    }

public static void GetPersonen(string token)
        {
            var httpRequest = (HttpWebRequest)WebRequest.Create(string.Format("{0}&client_id={1}&client_secret={2}", EmployeesURL, Client_id, Client_secret));
            httpRequest.Accept = "application/json";
            httpRequest.Headers["Authorization"] = "Bearer " + token;


            var httpResponse = (HttpWebResponse)httpRequest.GetResponse();
            using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
            {
                var jsonData = streamReader.ReadToEnd();

               
                JObject jObject = JObject.Parse(jsonData);

                foreach (var data in jObject["data"])
                {
                    foreach (var attributes in data["attributes"])
                    {
                        var firstname = attributes.SelectToken("first_name");
                        var value = firstname.SelectToken("value");
                        Console.WriteLine(value.Value<string>("value"));
                    }

                }
            }
        }

string.Format("{0}&client_id={1}&client_secret={2}", EmployeesURL, Client_id, Client_secret)

public static void GetPersonen(string token)
        {
            var httpRequest = (HttpWebRequest)WebRequest.Create(string.Format("{0}&client_id={1}&client_secret={2}", EmployeesURL, Client_id, Client_secret));
            httpRequest.Accept = "application/json";
            httpRequest.Headers["Authorization"] = "Bearer " + token;


            var httpResponse = (HttpWebResponse)httpRequest.GetResponse();
            using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
            {
                var jsonData = streamReader.ReadToEnd();


                var mitarbeiter = System.Text.Json.JsonSerializer.Deserialize<Mitarbeiter>(jsonData);
                Console.WriteLine(mitarbeiter.data.attributes.first_name.value);
            }
        }

public class Mitarbeiter
    {
        public string success { get; set; }
        public Data data { get; set; }
    }

    public class Data 
    {
        public string type { get; set; }
        public Attributes attributes { get; set; }
    }

    public class Attributes
    {
        public string type { get; set; }
        public Id id { get; set; }
        public FirstName first_name { get; set; }
    }

    public class Id
    {
        public string label { get; set; }
        public int value { get; set; }
        public string type { get; set; }
        public string universal_id { get; set; }
    }

    public class FirstName
    {
        public string label { get; set; }
        public string value { get; set; }
        public string type { get; set; }
        public string universal_id { get; set; }
    }

public class Mitarbeiter
    {
        public bool success { get; set; }
        public Data data { get; set; }
    }