Push API (Web Push) + Service Worker

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Добрый день. Которую неделю бьюсь (безуспешно) над попыткой получить сообщение с сервера. Вроде и Service Worker регистрируется, вроде и сервер подтверждает успешную регистрацию... А сообщения не доходят. Очень нужна помощь.
P.S. Код клиента должен работать в Gecko 48 (старый Firefox), который например не знает функций async/await и т.д.

Итак, есть код index.js

function urlBase64ToUint8Array(base64String) {
  var padding = '='.repeat((4 - base64String.length % 4) % 4);
  var base64 = (base64String + padding)
    .replace(/\-/g, '+')
    .replace(/_/g, '/');
 
  var rawData = window.atob(base64);
  var outputArray = new Uint8Array(rawData.length);
 
  for (var i = 0; i < rawData.length; ++i) {
    outputArray[i] = rawData.charCodeAt(i);
  }
  return outputArray;
}
 
 
var convertedVapidKey = urlBase64ToUint8Array(
      'BNat99ai8SavGs2qUy6AS_UggxI6KwyYcarPRQNkSWMLegNc8a0hcBdRPlJ8y_JMVHuSqofk0xBtoyvbYHWM1g8'
    )
 
 
navigator.serviceWorker.register('service.js').then(
  function(serviceWorkerRegistration) {
    serviceWorkerRegistration.pushManager.subscribe(
    {
    applicationServerKey: convertedVapidKey,
    userVisibleOnly: true
            }
    ).then(
      function(pushSubscription) {
        console.log(pushSubscription);
        
var info = {subscription: pushSubscription}     
        
var url = 'http://202.182.101.31:4000/save-subscription';
 
var xhr = new XMLHttpRequest({mozSystem: true});
 
xhr.open("POST", url, true);
xhr.setRequestHeader("Content-Type", "application/json");
xhr.onreadystatechange = function () {
    if (xhr.readyState === 4 && xhr.status === 200) {
        var json = JSON.parse(xhr.responseText);
        console.log(json);
        console.log('push service subscription successfull: ' + JSON.stringify(pushSubscription));
    } 
};
 
var data = JSON.stringify(info);
xhr.send(data);
                
      }, function(error) {
        console.log(error);
      }
    );
  });

код service.js

self.addEventListener('push', function(event) {
console.log("event");
  event.waitUntil(
    self.registration.showNotification('ServiceWorker Cookbook', {
      body: 'Alea iacta est',
    })
  );
});
 
self.addEventListener('activate', function(active) {
  console.log("active");
})

При запуске в консоле вроде все ок.

active
service.js:11:3
PushSubscription { endpoint: "https://updates.push.services.mozilla.com/wpush/v2/gAAAAABfLjasOeeW-nnReeKSFRxNZ4PmSSgDsvUaBiQttqhi-KwSxauPaxJNKZdISfzlI8nD9WLdoM0yrbzFshAfZRhmEeUSmGkhCrbRB1RvyW2qlsYgGsxDa5CY-A4X_-DboBVVuKBriEMeUWT2eRISASSbCS2bCSLPxufNgLDetPm6gYOAvm0", options: PushSubscriptionOptions }
index.js:37:9
Object { message: "success" }
index.js:53:3
push service subscription successfull: {"endpoint":"https://updates.push.services.mozilla.com/wpush/v2/gAAAAABfLjasOeeW-nnReeKSFRxNZ4PmSSgDsvUaBiQttqhi-KwSxauPaxJNKZdISfzlI8nD9WLdoM0yrbzFshAfZRhmEeUSmGkhCrbRB1RvyW2qlsYgGsxDa5CY-A4X_-DboBVVuKBriEMeUWT2eRISASSbCS2bCSLPxufNgLDetPm6gYOAvm0","keys":{"auth":"gOP1jIP_lRhGdOCqtJRsGQ","p256dh":"BDYnBhhzBpLnhIQWD6QhHZSaX1BcAX4h-6SwYAuleHOTjY-yTq1HnBqHtiM_DqRfkG-NuX9kxi2g2uD4Xs-LZLc"}}

Но, если я запускаю http://202.182.101.31:4000/send-notification сообщение не поступает, ходя написано { message: 'message sent' }

P.S. Код сервера (который отправляет):

const express = require('express')
const cors = require('cors')
const bodyParser = require('body-parser')
const webpush = require('web-push')
const app = express()
app.use(cors())
app.use(bodyParser.json())
const port = 4000
app.get('/', (req, res) => res.send('Hello World!'))
const dummyDb = { subscription: null } //dummy in memory store
const saveToDatabase = async subscription => {
  // Since this is a demo app, I am going to save this in a dummy in memory store. Do not do this in your apps.
  // Here you should be writing your db logic to save it.
  dummyDb.subscription = subscription
}
// The new /save-subscription endpoint
app.post('/save-subscription', async (req, res) => {
  const subscription = req.body
  await saveToDatabase(subscription) //Method to save the subscription to Database
  res.json({ message: 'success' })
})
const vapidKeys = {
  publicKey:
    'BNat99ai8SavGs2qUy6AS_UggxI6KwyYcarPRQNkSWMLegNc8a0hcBdRPlJ8y_JMVHuSqofk0xBtoyvbYHWM1g8',
  privateKey: 'hlHd0rrSPSSCJgrKoG0NLoJGI_Wyfi_d4hjxr71Txps',
}
//setting our previously generated VAPID keys
webpush.setVapidDetails(
  'mailto:myuserid@email.com',
  vapidKeys.publicKey,
  vapidKeys.privateKey
)
//function to send the notification to the subscribed device
const sendNotification = (subscription, dataToSend) => {
  webpush.sendNotification(subscription, dataToSend)
}
//route to test send notification
app.get('/send-notification', (req, res) => {
  const subscription = dummyDb.subscription //get subscription from your databse here.
  const message = 'Hello World'
  sendNotification(subscription, message)
  res.json({ message: 'message sent' })
})
app.listen(port, () => console.log(`Example app listening on port ${port}!`))

Помогите разобраться. Почему не получаю уведомления.