Xamarin Forms and Azure Mobile Service with Facebook authentication fails

Hi,

I've setup my app to authenticate to Facebook. Attached are the settings I've used. When we run the app and click on a button to authenticate to Facebook, it doesn't work and we get the error attached:

given url is not allowed by the application configuration.: one or more of the given urls is not allowed by the app's settings. it must match the website url or canvas url, or the domain must be a subdomain of one of the app's domains.

I've tried all kinds of combinations - but can't get it to work.

Has anyone had this experience and can they point me in the correct direction please?

Here's the line that I use to login (where's IMobileClient is a dependency to the iOS project and represents an azure mobile client instance):

            var fbUser = await DependencyService.Get<IMobileClient>().LoginAsync(MobileServiceAuthenticationProvider.Facebook);
            var dtm = DateTime.UtcNow;

thanks