Android Question REST Client Authorization Denied

using System;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
namespace resttest
{
    class Program
    {
        static void Main(string[] args)
        {
            Task t = new Task(HTTP_GET);
            t.Start();
            Console.ReadLine();
        }
        static async void HTTP_GET()
        {
            var TARGETURL = "http://www.XXXX.com:95/api/stores";
            HttpClientHandler handler = new HttpClientHandler();
           
            Console.WriteLine("GET: + " + TARGETURL);
            // ... Use HttpClient.           
            HttpClient client = new HttpClient(handler);
            var byteArray = Encoding.ASCII.GetBytes("XXX:XXX");
            client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));
            HttpResponseMessage response = await client.GetAsync(TARGETURL);
            HttpContent content = response.Content;
            // ... Check Status Code                               
            Console.WriteLine("Response StatusCode: " + (int)response.StatusCode);
            // ... Read the string.
            string result = await content.ReadAsStringAsync();
            // ... Display the result.
            if (result != null &&
            result.Length >= 50)
            {
                Console.WriteLine(result.Substring(0, 50) + "...");
            }
        }
    }
}

#Region  Activity Attributes
    #FullScreen: False
    #IncludeTitle: False
#End Region

Sub Process_Globals
    'These global variables will be declared once when the application starts.
    'These variables can be accessed from all modules.

End Sub

Sub Globals
    'These global variables will be redeclared each time the activity is created.
    'These variables can only be accessed from this module.
    Dim ObjectClass As String
    Dim LV As ListView
    
    Private Toolbar As Panel
    Private Caption As Label
    
End Sub

Sub Activity_Create(FirstTime As Boolean)
    'Do not forget to load the layout file created with the visual designer. For example:
    Activity.LoadLayout("ListHandlerLayout")

End Sub

Sub Activity_Resume

End Sub

Sub Activity_Pause (UserClosed As Boolean)

End Sub

Sub BuildList(URL As String, OClass As String)
    'ToastMessageShow(URL & "  " & ObjectClass, True)
    
    Dim Job As HttpJob
    
    LV.Clear
    ObjectClass = OClass
    
    Job.Initialize("ListJob", Me)
    
    Job.Username = Main.manager.GetString("Login")   
    Job.Password = Main.manager.GetString("Password")

    Job.Download(URL)
    
    Wait For (Job) JobDone(Job As HttpJob)
    
    If Job.Success Then
        FillListView(Job.GetString)
    Else
        Log("Job Failed: " & Job.ErrorMessage)
        ToastMessageShow("Job Failed: " & Job.ErrorMessage, True)
    End If   
    Job.Release
    
End Sub


Sub LV_ItemClick (Position As Int, Value As Object)
    ToastMessageShow(Value, True)
End Sub

Sub FillListView(Data As String)
    Dim JP As JSONParser
    JP.Initialize(Data)
    
    Caption.Text = ObjectClass
    Dim root As List = JP.NextArray
    For Each colroot As Map In root
        Dim Id As String = colroot.Get("Id")
        Dim Name As String = colroot.Get("Name")
        
        LV.SingleLineLayout.Label.TextColor = Colors.Black
        LV.AddSingleLine2(Name, Id)
    Next
    
End Sub

    Dim su As StringUtils
    Dim login As String = $"${Main.manager.GetString("Login")}:${Main.manager.GetString("Password")}"$
    Dim Job As HttpJob
    Job.Initialize("ListJob", Me)
  Job.Download("URL")
    Job.GetRequest.SetHeader("Authorization","Basic "&su.EncodeBase64(login.GetBytes("ASCII")))
    Wait For (Job) JobDone(Job As HttpJob)
    
    If Job.Success Then
    Else
        Log("Job Failed: " & Job.ErrorMessage)
        ToastMessageShow("Job Failed: " & Job.ErrorMessage, True)
    End If
    Job.Release

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Newtonsoft.Json;
using System.Net.Http;
using System.Collections.ObjectModel;
using System.Net.Http.Headers;

namespace XApp
{
    public class Stores
    {
        public string Id { get; set; }
        public string Name { get; set; }
        public string CustomerRSN { get; set; }
        public string RegionRSN { get; set; }
        public string ZoneRSN { get; set; }
    }

    public partial class MainPage : ContentPage
    {
        private const string url = "http://xxxxxx/api/stores";
        private HttpClient _Client = new HttpClient();       
        private ObservableCollection<Stores> _store;

        public MainPage()
        {
            InitializeComponent();
        }

        protected override async void OnAppearing()
        {
            var authData = string.Format("{0}:{1}", "xxxxx", "xxxxx");
            var authHeaderValue = Convert.ToBase64String(Encoding.UTF8.GetBytes(authData));
            _Client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authHeaderValue);

            var content = await _Client.GetStringAsync(url);
            var store = JsonConvert.DeserializeObject<List<Stores>>(content);
            _store = new ObservableCollection<Stores>(store);
            The_List.ItemsSource = _store;
            base.OnAppearing();
        }
    }
}