I need community help. I spent months in an IOT solution. HW/Firebase/IOS application is completed just missing the notification part. I succeeded by “message campaign” in firebase to send a notification to my IOS mobile, so it seems the whole notification path is correct.

But I can’t succeed to send a notification to users when a firebase data is updated.
Firebase structure is the following:

Sensors:
-ID1
-data (notification to send to user1 and User2 when changed)
-email User1 (User is signup in firebase)
-email User2 (User is signup in firebase)
-ID2
-data (notification to send to user1 and User2 when changed)
-email User1 (User is signup in firebase)
-email User2 (User is signup in firebase)

exemple: if for ‘ID1’ the data changed I want to inform the User1 and user2 of this update. How can I do it ?

I tried to manage this by “Google Function” but since this is new for me I didn’t succeed after many days of tutorial / doc etc.. I installed the tools in on my Mac. But I can t find any information how to do it. I looked for Javascript but no solution. thank you if someone could unblock me