on authcompleted what to navigate to main landing page get below error

I am able to successfully authenticate the user ; now i want navigate to page called page1; i tried different method with no luck one of then ( await Navigation.PushAsync(new Page1(),false);) got below error;

            await store.SaveAsync(account = e.Account, Constants.AppName);
            await Navigation.PushAsync(new Page1(),false);

            //MainPage = new NavigationPage(new Page1());

            //await DisplayAlert("Email address", user.Email, "OK");

        }

Unhandled Exception:

System.InvalidOperationException: PushAsync is not supported globally on Android, please use a NavigationPage.

Any help appreciated.