Messages successfully sent, but no notifications visible in Firebase Cloud Messaging - firebase

Question

Messages are reported as successfully sent, but no pop-up notifications appear.
With onMessage it is sometimes possible to log the message.
Requesting an FCM token only works on localhost.
When tried on the .com site, the error message depends on whether I use the PC or chromebook - the error messages generated are different.
I have used 2 different devices, but always Chrome browser. The cloud function writes the message and the FCM response to the function log, so it confirms success in sending.
When I deleted onMessage from the recipient webpage there was no sign of any notification.
The webpage is open during these trials. This is web/javascript.
Notification permission is set to allow, in both devices.
I have spent hours on web searches trying to find any hint as to what to try.
firebase-messaging-sw.js
importScripts('https://www.gstatic.com/firebasejs/3.9.0/firebase-app.js');
importScripts('https://www.gstatic.com/firebasejs/3.9.0/firebase-messaging.js');
firebase.initializeApp({
'messagingSenderId': '593287500713'
});
const messaging = firebase.messaging();
the relevant code which runs with the webpage
messaging.onMessage(function (payload) {
console.log('Message received. ', payload);
});
I assume that without onMessage, the notifications should appear based on the Firebase SDK, but they don't. WRONG ASSUMPTION
When in the background, nothing appears. (I think notifications are supposed to appear automatically.)
I can request and receive an FCM token when running on local host but the same code throws an error when deployed. "Request is missing required Authentication..."
I have been in contact with support # Google who have assured me that this suggestion, and then another would 100% fix the problem. Nothing made any difference.
I have tried the code snippets in the Firebase docs and also github examples.
If I could find existing code that works, that would be a great start, because I think that finding a solution after about 40 hours of effort is hopeless.
Have I missed something obvious?
UPDATES....
I have found two reasons for not seeing notifications.
1) My PC had a setting which seems to have partially suppressed the display. Unexpected because YouTube notifications do display. (Open notification tray on far right bottom of screen. "focus assist" with a crescent moon symbol. If when clicked it says "on" or "alarms only" I think this restricts what is seen.)
2) My assumption based on the Firebase docs and video was that onMessage() is to prevent notifications when the user is on the webpage and to allow the developer to ignore or handle the notifications within the page. Half right. Apparently the notifications are default ignored UNLESS onMessage() does something with them. The docs give snippets of code for onMessage() but only how to log to the console.
Also, found an amusing problem. Now that my PC has registered the recipient of the messages, it receives them even if that recipient is signed out and has signed in on another device. That sounds like a problem.
The currently working version of the code. This goes in the webpage / app (NOT in the messaging-sw.js file

Answer 1

The introductory video to messaging suggests that it is bad UX to have notifications from a website popping up when someone is on the website. Therefore the code can include onMessage() to either ignore the notification or to handle it within the page.
The docs give a version of onMessage that just logs the notification to the console and has just a comment about doing something else.
Other parts of the docs explain that the system automatically displays notifications.
Therefore I inferred that without onMessage() the notifications would appear automatically.
It seems I was wrong.
It has taken me a massive amount of time to figure this out and to find some code to make the notifications appear. (Even now I am not sure I have grasped what is happening, but the following seems to work)
This goes in the web page / app. (Not in the messaging-sw.js. Putting it there will throw an error "using window methods")
[Do note that I also found my PC was set in a way that seemed to allow YouTube to send notifications, but was preventing the display of FCM notifications. (See explanation in question)
So far I have tested this when the use has the webpage open, the webpage in the background and when the browser is closed. Notifications appear with the default sound and are listed in the notification tray.
This also happens if the recipient is signed out of the webpage and signed in on another device.. the messages continue to go to the same device.
Messages go to devices not to users]
messaging.onMessage(function (payload) {
try{ //try???
console.log('Message received. ', payload);
noteTitle = payload.notification.title;
noteOptions = {
body: payload.notification.body,
icon: "typewriter.jpg", //this is my image in my public folder
};
console.log("title ",noteTitle, " ", payload.notification.body);
//var notification = //examples include this, seems not needed
new Notification(noteTitle, noteOptions);//This can be used to generate a local notification, without an incoming message. noteOptions has to be an object
}
catch(err){
console.log('Caught error: ',err);
}
});
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