I’m somewhat new to FCM and Push Notifications in Flutter, so I currently thought about the following setup, but am stuck with 3 final questions.

In my Flutter app among other functions there is the one for users to write posts, and I would like every time a post is published all the other people receive a notification that a post has been published by a user (and username appears) , like “user_00293 just posted”. To turn on notifications in my Flutter app I need a server key, and it’s currently turned off. I saw on the internet that to activate it I have to go to the API section and press the “enable” button. In reality, all the Firebase APIs are already activated for me, and in fact the “manage” button appears. However, the server key still does not appear and if I try to go to the recommended Google Cloud page I get the following error message: Failed to load.

I am doing one flutter-related course, where I am working on a messaging application and I now want to notify the current user about the new message, I have checked many videos, posts but nothing helped, or mainly there are mostly about group chats, but I want for one-on-one messaging app, just like WhatsApp, And I have this code but I don’t know how to show the notification and I do have fcm token inside the firebase firestore “users” collection for each user along with their other details.

I develop a flutter app with firebase for iOS and Android. One feature of the app is that the user can set a reminder for a specific time or repeat interval and at that time a notification should appear. As the user can log in on multiple devices, the notification should appear on all devices. To achieve this, I was thinking about 2 options: