How to obtain an access token utilizing REST API?

[Don-Bot]

I am looking to generate an access token that I can then utilize to edit/create datasets and reports in the power bi service. I came across this link but after attempting to use it I am getting the below error messages I am having problems resolving.

Can someone point me in the correct direction?  Below is the code I've attempted to use and the error messages I am receiving. 

using System;
using Microsoft.IdentityModel.Clients.ActiveDirectory;

namespace walkthrough_push_data
{
    class Program
    {
        private static string token = string.Empty;

        static void Main(string[] args)
        {
            // Get an authentication access token
            token = GetToken();
        }

        private static async Task<string> GetToken()
        {
            string clientID = "{Client_ID}"; // The client id that Azure AD created when you registered your client app.
            string redirectUri = "https://login.live.com/oauth20_desktop.srf"; // RedirectUri you used when you register your app.
            string resourceUri = "https://analysis.windows.net/powerbi/api"; // Resource Uri for Power BI API
            string authorityUri = "https://login.microsoftonline.com/common/"; // OAuth2 authority Uri

            AuthenticationContext authContext = new AuthenticationContext(authorityUri);
            var result = await authContext.AcquireTokenAsync(resourceUri, clientID, new Uri(redirectUri));

            Console.WriteLine(result.AccessToken);
            Console.ReadLine();

            return result.AccessToken;
        }
    }
}

[lbendlin]

Have you completed the app registration including asking for the right scope?