OAuth2.0 throws invalid_grant type message while fetching the tokens from Xamarin forms Android app

I am using OAuth2.0 in my xamarin application and when i try to get the access token using the OAuth settings mentioned below I am able to get the access token, post my image on dropbx and everything works fine.

Configurations used in OAuth2.0

private const string Dbx_ClientId = "DROPBOX-APP-CLIENT-ID";
private const string Dbx_Secret = "DROPBOX-APP-CLIENT-SECRET";
private const string Dbx_AuthUrl = "https://www.dropbox.com/oauth2/authorize";
private const string Dbx_AccessTokenUrl = "https://api.dropboxapi.com/oauth2/token";
private const string Dbx_CallBack = "https://www.dropbox.com/callback";

The library used to do the OAuth2.0 call from Xamarin app is Xamarin.Auth version 1.5.0.3.

It's just I don't know why it shows an invalid_grant message to the user before it does that. I am doing the same thing in iOS and over there it never shows this message however when am working with android it shows this message. 

Do i need to pass something else when am trying to call the service through android?

 Please let me know what's the right way of doing this to avoid seeing the invalid_grant messages.