how to reference already initialized firebase

I am not sure about Integrate pro plugin, how it was designed. I tried with Integrate firebase (free version), in my website even though it showed warning firebase login worked. Including firebase messaging script in “integrate firebase” will enqueue but if we comment out enqueue of firebase scripts in this “push notification” plugin will create problem because sometime plugin scripts will load fast based on server usage, if push notification loads before integrate firebase it will throw error saying firebase app not initialized. It is better to include entire Firebase features in a single plugin, it takes more effort. If you need to send one time push notifications without firebase then please try other plugin Perfectly push (search in plugin repository) which uses VAPID key (self generated key) without firebase but it requires server changes to enable php gmp extension in php.ini file as push notification sent without any external server, i am not sure whether perfectly push is based on Buddypress. Please try that plugin if you need to send one time push notifications. I will update you later after completing or integrating other Firebase features in this plugin like I said in my previous reply.

I viewed your website and i found only 3 firebase scripts are enqueued by integrate firebase pro

https://www.gstatic.com/firebasejs/8.2.8/firebase-app.js?ver=2.6.0' id='firebase_app-js'
https://www.gstatic.com/firebasejs/8.2.8/firebase-auth.js?ver=2.6.0' id='firebase_auth-js
https://www.gstatic.com/firebasejs/ui/4.7.3/firebase-ui-auth__en.js?ver=2.6.0' id='firebase_ui-js'

firebase database and firestore firebase files are missing and not enqueued by “integrate firebase pro”, Please make sure enqueue all firebase files are enqueued like in free version of Integrate firebase plugin,
Below 2 files are not enqueued due to this you are getting firebase-database error

https://www.gstatic.com/firebasejs/8.2.5/firebase-database.js?ver=0.8.0'

'https://www.gstatic.com/firebasejs/8.2.5/firebase-firestore.js?ver=0.8.0'

I enabled both those scripts and the plugin still makes my firebase ui web login disappear and my firebase data disappear

does the app id need to be the same as the one used in integrate firebase pro or can it be different?

Please use same Firebase app credentials used in this Push notification for post and Buddypress plugin for Firebase integrate plugin
Both plugins firebase credentials needs to be same.
I have already tested using Firebase integrate free version plugin and email login is working along with this plugin, Attached below are screenshots
Firebase integrate login and this plugin test
I have also given details in plugin’s support url
Firebase integrate plugin along with push notification for post and buddypress plugin

I tried it. It still makes my firebase login disappear and it makes my firebase data no longer show. I even tried disabling analytics and storage in the integrate firebase plugin. it still interferes. i really wish we could figure this out i do not know why it is impossible for me to impliment push notifications like every other website in the world.

i can email you the pro plugin if you want to take a look

Basically, this push notification plugin uses only firebase-app core file and firebase-messaging core file to send notifications, this is not related to firebase-ui core file. I sent you a message from your website, please check it.