What is wrong with this Lighthouse audit? Can I install a PWA from http://localhost

I have a PWA that passes the Lighthouse audit on Chrome for an installable PWA but I never get prompted to install it and the "beforeinstallprompt" event never fires.

I am developing/debugging with http://localhost, which seems suitable for other tests, could this be the problem? I want to test my bespoke install prompt locally before deployment.

Manifest: -

{
  "short_name": "Brotkrumen",
  "name": "Brotkrumen Web App",
  "description": "Native Background Geolocation POC",
  "icons": [
    {
      "src": "gingerbreadhouse.png",
      "sizes": "48x48 128x128 144x144 192x192 512x512",
      "type": "image/png",
      "purpose": "any"
    },
    {
      "src": "gingerbreadhouse.png",
      "sizes": "48x48 128x128 144x144 192x192 512x512",
      "type": "image/png",
      "purpose": "maskable"
    }
  ],
  "start_url": "/travelmanager.html",
  "background_color": "#00ccdd",
  "theme_color": "#00ccdd",
  "display": "fullscreen"
}

Lighthouse Audit: -

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