项目是使用的 flutter，第一次接触原生 ios native，请教各位。

已经进行了的操作：
1 、apple 开发者账户网页添加了 push notification 证书
2 、xcode 里 runner target 的 capability 也打开了推送
3 、如下修改了 AppDelegate.swift （参考的官方文档）

但是真机测试并没有 print 出 token 值，就很疑惑，想请教是不是缺少了什么步骤，还是 AppDelegate.swift 写错了

import UIKit import Flutter  @UIApplicationMain @objc class AppDelegate: FlutterAppDelegate {     override func application(_ application: UIApplication,                                 didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?     ) -> Bool {         UIApplication.shared.registerForRemoteNotifications()         GeneratedPluginRegistrant.register(with: self)         return super.application(application, didFinishLaunchingWithOptions: launchOptions)     }          override func application(_ application: UIApplication,                                 didRegisterForRemoteNotificationsWithDeviceToken                                 deviceToken: Data) {         print(deviceToken)         sendDeviceTokenToServer(token: deviceToken)     } }  func sendDeviceTokenToServer(token: Data) {     let url = URL(string: "https://push.example.com/ios?token=" + String(decoding: token, as: UTF8.self))!      let task = URLSession.shared.dataTask(with: url) {(data, response, error) in         guard let data = data else { return }         print(String(data: data, encoding: .utf8)!)     }      task.resume() }