iPhone/iPad: open this page in Safari, tap Share → Add to Home Screen. Then open it from the Home-Screen icon and tap Enable.
It looks like notifications were previously denied. On iOS, remove the Home-Screen app, clear the site’s data (Settings → Safari → Advanced → Website Data), re-add to Home Screen, then try again.
Waiting for your action…All set! You can close this page.
Troubleshooting
If you blocked notifications before: re-enable in your browser’s Site settings. On iOS, you must run this page as a Home-Screen app; if you denied once, reinstall the app to reprompt.