Add to homescreen not showing in 2.1.5 version

I’ve installed plugin version 2.1.5 & also HTTPS is configured. Also the Manifest & Service Worker status is true. But I couldn’t able to get why “Add to Homescreen” option is not showing ?

It would be great, if we got any clue. I’ve also reached to forum, but didn’t get any convincing solution.

Thanks!

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