Why Activity Indicator Not working In Xamarin.forms?

I am trying to display ActivityIndicator After I press a button while I am trying to update The Column Field On DataBase, it is not appearing? What is the problem?

On the following My Code:

ActivityIndicator ai = new ActivityIndicator()
            {
                HorizontalOptions = LayoutOptions.CenterAndExpand,
                Color = Color.Black
            };
            ai.IsRunning = true;
            ai.IsEnabled = true;
            ai.BindingContext = this;
            ai.SetBinding(ActivityIndicator.IsVisibleProperty, "IsBusy");

            ProcessToCheckOut = new Button { Text = "Set Inf" };
            ProcessToCheckOut.Clicked += (object sender, EventArgs e) =>
            {
                this.IsBusy = true;
                UserUpdateRequest user=new UserUpdateRequest();
                user.userId = CustomersPage.ID;
                appClient.UpdateInfo(user);                  
                this.IsBusy = false;
                Navigation.PushAsync(new CheckoutShippingAddressPage(appClient));
            };
         Content = new StackLayout
            {
                Children={
                tb,
                ai,
                ProcessToCheckOut
                }
            };