Firebase推送通知fcmClient.SendAsync（message，cancellationToken）返回null

Question

对于IOS推送通知，我使用下面的代码并从c＃.net Windows Servervice运行

      var settings = FileBasedFcmClientSettings.CreateFromFile("c:\\fcm.json");
            // Construct the Client:
            using (var client = new FcmClient(settings))
            {
                var notification = new Notification
                {
                    Title = "message_tobeSent",
                    Body = "message_tobeSent",//change later
                }  
                // The Message should be sent to the News Topic:
                var message = new FcmMessage()
                {
                    ValidateOnly = false,
                    Message = new Message
                    {
                        Notification = notification,
                        Token = token //dynamic value
                    }
                };
                // Finally send the Message and wait for the Result:
                CancellationTokenSource cts = new CancellationTokenSource();
                // Send the Message and wait synchronously:
                var result = client.SendAsync(message, cts.Token).Result;

在上面的代码中，以下代码行返回了空值    client.SendAsync（message，cts.Token） 如果我从控制台应用程序运行相同的代码，则它的工作原理 请建议我，我想念的是什么？