从javascript客户端发送消息时未显示FCM通知

Question

我正在尝试使用JavaScript客户端通过FCM POST将HTTP消息发送到快速应用程序。该应用程序正在接收消息，但未显示任何通知，但是当我从通知编辑器发送消息时，该通知会出现在应用程序上。请找到javascript代码。我尝试了前台和后台通知在两种情况下都不会出现。  当我从javascript发送消息时，将调用以下委托：-

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any],
                 fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void)

JavaScript代码：-

function callAPI(token, i, tokenArrayLength){
var data = JSON.stringify({
    "to": token,
    "content_available": true,
    "data": {
      "message": Desc.value + "\nClick To know more about the event",
      "title": Title.value 
    }
  });

  var xhr = new XMLHttpRequest();
  //xhr.withCredentials = true;

  xhr.addEventListener("readystatechange", function () {
    if (this.readyState === 4) {
      console.log(this.responseText);
      if(i == tokenArrayLength-1){

        //window.location.reload();

      }
    }
  });

  xhr.open("POST", "https://fcm.googleapis.com/fcm/send");
  xhr.setRequestHeader("authorization", "key=AIzaSyDzbJ********");
  xhr.setRequestHeader("content-type", "application/json");
  xhr.setRequestHeader("cache-control", "no-cache");
  //xhr.setRequestHeader("postman-token", "668*******");

  xhr.send(data);

}