Challnege not redirecting to Okta Login page

On clicking Okta Login the challnege is not redirecting to Okta login page and isntead redirects back to the application login page only. The application uses FormsAuthentication and now i am integrating Okta.

Its an MVC 5 App in version 4.6.2. Below are my code snippets .

Can someone guide what i am doing incorrect.