here is the response from OneSignal:

 there,

I took a look at https://www.mistergadget.tech/ and could see the following error in console. ----- [Service Worker Installation] Installing service worker failed SecurityError: Failed to register a ServiceWorker: The origin of the provided scriptURL ('https://d8c7r9c5.rocketcdn.me') does not match the current origin ('https://www.mistergadget.tech'). -----

Some of the files our WordPress plugin automatically includes in your page is being re-written by your server to be served from a Content Delivery Network (CDN). Due to browser restrictions on web push, these files must actually not be re-written and have to be served from the same site domain users are accessing your site from:

• yoursite.com/wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKWorker.js.php

• yoursite.com/wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKUpdaterWorker.js.php

If you're using WP Super Cache, W3 Total Cache, WP Engine, or a similar caching plugin, please see Troubleshooting Web Push - WordPress CDN Support.

Let us know which CDN plugin you are using if you are still having issues.

Thanks

I have tried to install onesignal push notifications solution, but it works with some problem.

I have contacted the onesignal support, here is the answer

“Unfortunately your WordPress Theme doesn't appear to support the wp_head hook: https://developer.wordpress.org/reference/hooks/wp_head/

This is required for any code to be loaded in the head tags of the site (which is where our code needs to be to work properly).

Are you able to contact your theme developer and ask them for assistance adding this or how you can make sure this code works?”

can you confirm it’s not supported?

Thank you!

Happy holidays!