Progressive Web App – Service Worker not serving start_URL

Noted from Register A service worker,

If we register the service worker file at /example/sw.js, then the service worker would only see fetch events for pages whose URL starts with /example/ (i.e. /example/page1/, /example/page2/).

Inline with the shown error and given in this documentation, check the following:

1. Define a start_url property in your manifest.json file.
2. Ensure that your service worker properly caches a resource that matches the value of start_url.

Also, check this tutorial and see if it will help you.