Invalid topic name while calling watch() from c#

Question

I have a topic with all permission and subscription. from google cloud console I can list my topics. BUT from c# code, or TRY IT page am getting invalid topic name. I have created a project enabled pub/sub api create topic created subscription granted permission created api keys am getting unread messages from gmail, that means the key is working fine. but cant get topic name here is my 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 System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Google.Cloud.PubSub.V1;
namespace ConsoleApplication4
{
class Program
{
    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_secret2.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,
                "user",
                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");

        List<Message> result = new List<Message>();
        UsersResource.MessagesResource.ListRequest request = 
service.Users.Messages.List("me");
        request.Q = "is:unread";

        do
        {
            try
            {
                ListMessagesResponse response = request.Execute();
                result.AddRange(response.Messages);
                request.PageToken = response.NextPageToken;
            }
            catch (Exception e)
            {
                Console.WriteLine("An error occurred: " + e.Message);
            }
        } while (!String.IsNullOrEmpty(request.PageToken));
        foreach (Message m in result)
        {
            Message m2 = service.Users.Messages.Get("me", m.Id).Execute();
            Console.WriteLine("Message: {0}", m2.Snippet);
        }

        WatchRequest body = new WatchRequest()
        {
            TopicName = "projects/test/topics/topicTest",
            LabelIds = new[] { "INBOX" }
        };
  string userId = "me";
        UsersResource.WatchRequest watchRequest = service.Users.Watch(body, 
userId);
        WatchResponse test = watchRequest.Execute();
        Console.Read();
    }
    }
}