Here are some of the most common reasons, why you are unable to see the opt-in dialog box on your website.
Might have already approved permissions
There might be a possibility that you've already given the site permissions by either following these
It is possible to manually change permissions in Firefox on Desktop. Click the lock icon next to the URL in the address bar. After this, you will see the permissions tab with Receive Notifications option. Allow for push notifications and to remove notification permissions, click the close button next to Allow button.
To manually manage web push notification permission settings for a website in Safari on OSX (mac),
Follow the path Safari -> Preferences -> Notifications in the primary navigation bar.
Change a site's permissions by approving, denying or remove it all together.
Browser does not support push notification
Web browser push notifications are available on Safari, Firefox, and Chrome. Visitors on unsupported devices will see your site as normal but won’t be able to see the opt-in dialog box.
If manifest.JSON file is already present
Web Push notification prompts will not appear if a manifest.JSON file is already present on the rarely. This happens very rarely but may conflict with PushAssist manifest.JSON file.