Pinterest Authentication Problem

Hi,
We have working on Social account Authentication API like Facebook,Twitter,Instagram etc. All other many social accounts API are working fine. but we have facing the problem with Pinterest API, its not working fine.
Here is my code that we have using :

void AuthPinterest()
{
var auth = new OAuth2Authenticator (
clientId: "",
clientSecret: "",
scope: "read", // read_write
authorizeUrl: new System.Uri ("https://pinterest.com/oauth/authorize/"),
redirectUrl: new System.Uri ("https://test.com"),
accessTokenUrl: new System.Uri ("https://pinterest.com/oauth/access_token/")
);
auth.AllowCancel = true;
auth.Completed += delegate(object sender, AuthenticatorCompletedEventArgs e)
{
if(e.IsAuthenticated)
{

            }
            DismissViewControllerAsync (true);
            App.SuccessfulLoginAction.Invoke ();
        };
        UIViewController vc = auth.GetUI ();
        PresentViewController (vc, true, null);
    }

we did not find any solution. Please help.

Thanks