hi ,

im working on a function that will save the attachment file in Email via Gmail using gmail API code(C#).

but i keep getting an error that saying : 

An unhandled exception of type 'Google.Apis.Auth.OAuth2.Responses.TokenResponseException' occurred in Google.Apis.dll

Additional information: Error:"unauthorized_client", Description:"", Uri:""

here is the code :

using Google.Apis.Auth.OAuth2;
using Google.Apis.Gmail.v1;
using Google.Apis.Gmail.v1.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using AE.Net.Mail;

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace GmailQuickstart
{
    class Program
    {
        // If modifying these scopes, delete your previously saved credentials
        // at ~/.credentials/gmail-dotnet-quickstart.json
        static string[] Scopes = { GmailService.Scope.GmailReadonly };
        static string ApplicationName = "Gmail API .NET Quickstart";

        static void Main(string[] args)
        {

            UserCredential credential;

            using (var stream =
                new FileStream("client_secret.json", FileMode.Open, FileAccess.Read))
            {
                string credPath = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
                credPath = Path.Combine(credPath, ".credentials/gmail-dotnet-quickstart.json");

                credential = GoogleWebAuthorizationBroker.AuthorizeAsync(GoogleClientSecrets.Load(stream).Secrets, Scopes, "Sapir", CancellationToken.None, new FileDataStore(credPath, true)).Result;
                Console.WriteLine("Credential file saved to: " + credPath);
            }

            // Create Gmail API service.
            var service = new GmailService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });

            // Define parameters of request.
            UsersResource.LabelsResource.ListRequest request = service.Users.Labels.List("me");

         
            IList<Label> labels = request.Execute().Labels;
            Console.WriteLine("Labels:");
            if (labels != null && labels.Count > 0)
            {
                foreach (var labelItem in labels)
                {
                    Console.WriteLine("{0}", labelItem.Name);
                }
            }
            else
            {
                Console.WriteLine("No labels found.");
            }
            Console.Read();

        }
    }
}

can you please help me know what is the problem ?

thank you