I have used the manifest generator and validated its functionality.

When I browse to my site: https://mysite.com the install banner does not appear. Probably because I do not have a 'service worker'. Need guidance on this.

Second, when I click the plus sign I can add the app to the home screen, but the home screen never shows the icon, nor is it full screen. Still have the address bar and the browser controls at the bottom.

Here is the manifest:
{
"lang": "en",
"background_color": "#ffffff",
"name": "go BillThis - mobile business management",
"short_name": "go BillThis",
"display": "fullscreen",
"icons": [
{
"src": "/Images/bt144.png",
"sizes": "144x144",
"type": "image/png"
}
]
}