App does not open Okta login page while Making login request form Xamarin forms app

I have created a Xamarin forms App integrated okta login with the following guide

The problem I am facing is First time when I made login request it redirects to the okta login page but the second time it does not redirect to okta login page it fetches from the browser caches (that’s what I think).
Is there any way that when we are making Authorisation Request to okta login it always ask for Username and password?
I tried to setPrompt to login in Android it works but in iOS it is not working
Kindly let me know as soon as possible.