Firebase organizes groups of similar apps into "projects." For example, it’s a good best practice to put the Android and iOS variations of an app into the same group (or "project") in Firebase.
Apps in the same project can access each other's data about users and their behavior, giving you an overall picture of how your customers use your apps.
Existing apps and projects
If you've used Firebase before or if you've already linked some of your AdMob apps, you may have existing projects and apps in your Firebase account. When you link an app, AdMob will try to match the app you're linking to an existing app or project in your Firebase account. If a match is found, you will have the option to link your AdMob app to the existing app or project or create a new one.
Project limits
Each Firebase account has a set limit to the number of projects the account may create. If the limit has been reached, you'll receive an error when you try to link an AdMob app to a new project.
When you've reached the project limit, you can still link your AdMob apps to Firebase by selecting an existing project.
Naming constraints
Each project name must adhere to the following rules:
- From 4 to 30 characters in length
- Only contains letters, numbers, spaces, and the following characters: - ' " !
- Doesn't contain double-width, regional, or accented characters