Enable the Firebase API resources you're going to use from the Firebase Console
Log into your Firebase Console and enable the resources you'll use for your application, like Authentication, Firestore, etc.
This video is part of a playlist that helps you create your first Ionic Application from scratch, it will help you understand about:
Ionic Components.
Ionic Navigation.
Displaying Data on the Screen.
Connecting your Application to Firebase's Firestore database.
The playlist is based on Firebase's new Modular Web SDK.
You can access the full playlist here:
• Firebase Modular Web SDK