These tips from https://developers.google.com/web/fundamentals/primers/service-workers/lifecycle.
A service worker won't receive events like fetch and push until it successfully finishes installing and becomes "active".
Use this knowledge in combination with the next point.
By default, a page's fetches won't go through a service worker unless the page request itself went through a service worker. So you'll need to refresh the page to see the effects of the service worker.
So a service worker that wasn't installed initially, but has since been installed and actually become active, won't start handling fetch requests for the current page. You have to reload the page.