How to do automatic push notifications in android webview application with php mysql? (With Thunkable)

I'm developing an android application with a WebView that opens a website (which is the actual application) and I need to make that site or its server send automatic push notifications to the mobile phone that has the application (even without being open), once the user on one side does an action (via the php / javascript site), sends a notification to the intended recipient of the notification for example. I have already managed to generate a push notification for the android, but need to go to the notification api website and send it manually (obviously the user will not be doing this), the problem is in having the application in php send this notification to the mobile , I also know that you need to use FireBase. I do not handle a lot of android programming and I also do not find anything on the internet that solves my problem.