Here is my code //var token1 = await _tokenStore.GetAccessTokenAsync(Id);
//accessToken1 = token1.RefreshToken;
//var restClient1 = new RestClient("https://identity.xero.com/connect/revocation");
//var request1 = new RestRequest(Method.POST);
//string encoded = base64encode(Configuration["Xero:ClientId"] + ":" + Configuration["Xero:ClientSecret"]);
//request1.AddHeader("Authorization", string.Format("Basic {0}", encoded));
//request1.AddHeader("Content-Type", "application/x-www-form-urlencoded");
//request1.AddParameter("application/json", accessToken1, ParameterType.RequestBody);
//var response1 = restClient1.Execute(request1);