The problem is not in my code, but how you call the request

try with this

        string output = "";

        Task.Run(async () => { output = await ds.ReloadUsers(); });


        b.Clicked += async (sender, e) =>
        {
            await Application.Current.MainPage.Navigation.PushAsync(new ScanPage(output));
        };

Read as a memory stream, write to file, open the file.
The file operations and opening with the PDF reader will have to be platform specific. You can achieve this by creating interfaces which are called in your cross platform code and implemented for each platform using dependency injection.

Do you mean programmatically? Like the user has turned off mobile data, and you want your app to force it back on?

Your app shouldn't know the difference. Your app doesn't know if the internet is coming from WiFi or mobile data. That's handled completely anonymously from apps.

If your carrier is having a problem that's nothing your app can take care of. If your service doesn't include mobile data, there is nothing your app can do about that.

I got it resolved myself. Just in case if someone else also experiencing the same.
As the source of my graphics was from a secure (https) server therefore I needs to change the following settings.
Android Options => Advanced
HttpClient implementation = Set to "Managed" option value
SSL/TLS implementation = set to "Native TLS 1.2+" option value

@clopez
Dont know whether this helps:
Put this in the class(ViewModel,Page w/e) that receives the message in your case that would be the parent page.
MessagingCenter.Subscribe</*what you want to subscribe*/>(this, "MessageYouWantToSend", sender => { //whatever you want to do });

And then in the class that sends the message(Your case the child page) put this where you send the message, if you want to pass the value to the previous page after closing the page you should put it in the OnBackButtonPressed(override) something like this:
protected override void OnBackButtonPressed() { base.OnBackButtonPressed(); MessagingCenter.Send(this, "MessageYouWantToSend"); }

Hope it helped.

A much more cleaner way to send values to the previous page is the Messaging Center.
Google for Xamarin Messaging Center, I'm not allowed to post links yet
And it's possible to send it to all pages of your application, so you don't have to send it through pages.