I\'ve created a Progressive Web App. It\'s simple, just an index.html, a folder \"images\" with favicon etc, a sw.js et a styles.css
My code from manifest.json
Your site should be in https with a certificate, valid manifest along with a valid service worker showing in chromes application tab, all this makes your site qualified as basic PWA to add it as installable site (it gets created with a google on the fly signed .APK file)
When there is issue with https, certificate or service worker (most case this is the reason ) still an icon will be added to the home screen and will open as app without address bar. Difference is, it’s just a bookmark kind of link. It’s not a .apk file generated by WebApk in chrome. On such scenarios, chrome doesn’t shows the install banner.
Other case might be, it might have come and gone once without you noticin it or it reloaded the page on ur interruption. One first decline by user, chrome doesn’t show again. You can try from a different device and still same tho g happens, it’s one of ur PWA component not configured correctly as mentioned in first para.
Here and here are some official criteria from Google on install banners.