How to show listview in xamarin form

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C#

ListView

webservice

Xamarin

I try show listview with data json from web service but i got error in

var response = await api.getAllUserGoogle();

it is message error :

Response status code does not indicate success: 500 (Internal Server Error)

It is my data json from webservice

{"isSuccess":true,"resultMessage":"","data":
[{"password":"MnwPzyBdAZBrDV6xMHoIzg","userid":138,"email":"gusssion@gmail.com","username":"gussion"},{"password":"PFjQJkorLvR+ilWUWdq1Yw","userid":98,"email":"vania@gmail.com","username":"vania"},{"password":"LRmayI3ClJtVWijRyhR3Fg","userid":106,"email":"yuli@gmail.com","username":"yuli"}]{

It is my coding:

ApiInterface.cs

interface ApiInterface
    {
        [Post("/getAllUser")]
        Task<Data_ReturnResult> getAllUser();
    }

Data_ReturnResult

[Serializable]
    public class Data_ReturnResult
    {
        public Boolean isSuccess;
        public String resultMessage;
        public object data;

        public static Data_ReturnResult createReturnResult(Boolean isSuccess, String resultMessage, object data = null)
        {
            Data_ReturnResult result = new Data_ReturnResult();
            result.isSuccess = isSuccess;
            result.resultMessage = resultMessage;
            result.data = data;
            return result;
        }
        public static String createReturnResultInJson(Boolean isSuccess, String resultMessage, object data = null)
        {
            Data_ReturnResult result = createReturnResult(isSuccess, resultMessage, data);
            return JsonConvert.SerializeObject(result);
        }
    }

MainPage.xml

<StackLayout>

    <ListView
        x:Name="MyListView">
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextCell Text="{Binding Username}" TextColor="Black"/>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

</StackLayout>

MainPage.xaml.cs

public partial class MainPage : ContentPage
    {

        private ApiInterface api;
        public List<User> users { get; set; }
        
        public class User
        {
            String password;
            String userId;
            String email;
            String username;

            public string Password { get => password; set => password = value; }

            public string UserId { get => userId; set => userId = value; }

            public string Email { get => email; set => email = value; }

            public string Username { get => username; set => username = value; }
        }

        public MainPage()
        {
            InitializeComponent();

            api = RestService.For<ApiInterface>("http://192.168.0.185/webservice/webservice.asmx");
            _ = CallApi();
        }

        async Task CallApi()
        {
            var response = await api.getAllUsers();
            MyListView.ItemsSource = response.ToString();

        }

    }

WebService

[WebMethod]
        [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
        public void getAllUsers()
        {
            DbAccessConnection conn = getActiveConnection();

            if (conn == null)
                return;

            try
            {
                beginTransaction(conn);
                
                User users = new User(conn);
                DataSet ds = new DataSet();
                string tbName = "User";

                users.getAll(ds, tbName);
                DataTable dtTbl = ds.Tables[tbName];

                List<Dictionary<String, object>> lsOfDtTbl = Tools.convertDataTableToList(dtTbl);

                Responder.writeResponse(true, "", lsOfDtTbl );
                commitTransaction(conn);
            }
            catch (Exception ex)
            {
                rollbackTransaction(conn);
                Responder.writeResponse(false, ex.Message);
            }
        }

What I have tried:

Could you help me how to fix it ?