Why bluetooth UWP app during connection gives access is denied

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Devices.Bluetooth;
using Windows.Devices.Bluetooth.Rfcomm;
using Windows.Devices.Enumeration;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.Networking.Sockets;
using Windows.Security.Authorization.AppCapabilityAccess;
using Windows.Storage.Streams;
using Windows.UI.Popups;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using Windows.UI.Popups;
using Windows.Security.Authorization.AppCapabilityAccess;

// The Blank Page item template is documented at https://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409


namespace hfpuwp
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public static readonly Guid HFP_Id = new Guid("0000111f-0000-1000-8000-00805f9b34fb");


        public MainPage()
        {
            this.InitializeComponent();
        }

    private async void Button_Click(object sender, RoutedEventArgs e)
        {
            BluetoothDevice BlutooDevice;

            RfcommDeviceService BTService;

            StreamSocket BTSocket;

            DataWriter _writer;

            DataReader _reader;
            DeviceInformationCollection devices = await DeviceInformation.FindAllAsync(BluetoothDevice.GetDeviceSelectorFromPairingState(true));

            String xz = "";
            for (int i = 0; i < devices.Count; i++)
            {
                xz += devices[i].Name+" ";

                //Console.WriteLine(i + "#:    " + devices[i].Name + "    " + devices[i].Id);
                if (devices[i].Name == "OPPO F11 Pro")
                {
                    BTDevice.Text = devices[i].Name + " " + devices[i].Id;
                    try
                    {
                        BlutooDevice = await BluetoothDevice.FromIdAsync(devices[i].Id);
                        var result = await BlutooDevice.GetRfcommServicesForIdAsync(RfcommServiceId.FromUuid(HFP_Id));
                        if (result.Services.Count > 0)
                        {
                            var accessStatus = await BlutooDevice.RequestAccessAsync();
                            BTService = result.Services[0];
                            BTSocket = new StreamSocket();
                            if (result.Services.Count > 0 && accessStatus == DeviceAccessStatus.Allowed) {
                            await BTSocket.ConnectAsync(BTService.ConnectionHostName, BTService.ConnectionServiceName,
                                SocketProtectionLevel.BluetoothEncryptionAllowNullAuthentication);
                            }


                            //_writer = new DataWriter(BTSocket.OutputStream);
                            //_reader = new DataReader(BTSocket.InputStream);
                        }
                        BTDevice.Text = "Connection Sucessful";


                    }
                    catch (Exception ex)
                    {

                        Debug.WriteLine($"Failed to get Bluetooth device from ID {devices[i].Id}: {ex.Message}");
                        continue;
                    }
                }

            }
        }

    }

}