Notifications plugin

I have been chasing my tail trying to wrap my hands around aligning the sample code, the plug-in, the git-hub example pointed to by the plug-in docs and Google’s FCM (since GCM is depreciated).

The docs (Documentation>Developer Guides>Events/Listeners>Local/Push Notifications) show that all 3 states of the device are handled.  I see nothing referencing a Custom URL - that I thought was necessary to launch an app.  

[docs:]

Not running — the app has exited by design, user decision, reboot, etc. In this state, if the user interacts with the notification, the operating system will launch the app. Information about the notification event will be passed to the app using “launch arguments”. 

Dont we need a custom URL setup so that it knows what to load?

Unless I’m reading the sample app wrong, it appears to be sending itself a message - with everything tied to the googleRegistrationId - which I understand being needed for sending - but receiving? Nowhere do I see a phone number.

If the client app needs to register, where and when, and then how does the phone number get associated with their registration id - and as a sender, how do I get it?

Are the docs or sample code no longer current?

A point in the right direction would be appreciated. I’ve obviously missed something right in front of me.

Thanks in advance.