UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36

Steps to reproduce the problem:
I want to add to my app "Add To home screen banner", I went through the manual
https://developers.google.com/web/fundamentals/engage-and-retain/app-install-banners/#testing-the-app-install-banner

Have fulfilled the conditions

    Manifest file
    {
    "name": "Project clean as pwa",
    "short_name": "Pro Clean",
    "icons":[
    {
    "src": "/icons/icons8-washing-machine-48.png",
    "type": "image/png",
    "sizes": "48x48"
    },
    {
    "src": "/icons/icons8-washing-machine-96.png",
    "type": "image/png",
    "sizes": "96x96"
    },
    {
    "src": "/icons/app-icon-192x192.png",
    "type": "image/png",
    "sizes": "192x192"
    },
    {
    "src": "/icons/icons8-washing-machine-480.png",
    "type": "image/png",
    "sizes": "480x480"
    },
    {
    "src": "/icons/icons8-washing-machine-512.png",
    "type": "image/png",
    "sizes": "512x512"
    }
    ],
    "start_url":"/initial",
    "scope": "../",
    "display":"standalone",
    "orientation":"any",
    "background_color":"#fff",
    "theme_color":"#3f51b5",
    "description":"Simple dry clean description",
    "dir":"ltr",
    "lang":"en-US"
    }

    Registered service worker
    if("serviceWorker" in navigator){
    navigator.serviceWorker.register('/sw.js')
    .then(function(){
    console.log("Service worker registered");
    });
    };

    Added fetch event handler in serviceworker file
    self.addEventListener("fetch",function(event){
    event.respondWith(fetch(event.request));
    });

    Saving beforeinstallprompt event for later use
    window.addEventListener("beforeinstallprompt",function(event){
    console.log("beforeinstallprompt fired");//this never appears after waiting for long
    event.preventDefault();
    event.prompt();
    deferredPrompt = event;
    return false;
    });

    Using the event later
    function collectOrder(){
    console.log("Using the event ", deferredPrompt);//on call of the funtion the event comes undefined
    if(deferredPrompt){
    deferredPrompt.prompt();

     deferredPrompt.userChoice.then(function(choiceResult){
     	console.log(choiceResult.outcome);
     	if(choiceResult.outcome==="dismissed")
     		console.log("User cancelled installation");
     	else
     		console.log("User added to homescreen");
     });
     deferredPrompt = null;

    };
    }

The lighthouse test says the app is pass for "install banner"

What is the expected behavior?
The install banner should appear.

What went wrong?
The banner never appeared.

Did this work before? No 

Chrome version: 66.0.3359.181  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: