Error in accessing google sites feed by using service account c#

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C#

MVC

google-api

I am trying to access google sites feed by using google service account. But I get "The remote server returned an error: (403) Forbidden."(Not authorized to access this feed) error.

The code written is as follows:

var certificate = new X509Certificate2(filePath, password, X509KeyStorageFlags.Exportable);

var serviceAccountCredentialInitializer =new ServiceAccountCredential.Initializer("abc@developer.gserviceaccount.com")
{Scopes = new[] {"https://sites.google.com/feeds/"}}.FromCertificate(certificate);

var credential = new ServiceAccountCredential(serviceAccountCredentialInitializer);

if(!credential.RequestAccessTokenAsync(System.Threading.CancellationToken.None).Result)

throw new InvalidOperationException("Access token request failed.");

var requestFactory = new GDataRequestFactory(null);
requestFactory.CustomHeaders.Add("Authorization: Bearer " + credential.Token.AccessToken);

//SitesService class inherits MediaService

 SitesService service = new SitesService(null)
            {
                RequestFactory = requestFactory 
            };

Stream feed = service.Query(new Uri("https://sites.google.com/feeds/content/domain-name/site-name?path=page-path"));

I have also granted access to required scopes to google service account from admin panel. But still same error.

Can someone please tell me, what is wrong in my code?