Step 1: Open your Firebase Project.
Step 2: Click on the iOS icon to add an iOS app to your project.
Step 3: Enter your iOS App's Bundle ID. This is unique ID for your app. Write to firstname.lastname@example.org to get all your app's bundle IDs.
Step 4: Add a nick name for your app. It is recommended to your your App name here. Skip adding the App Store ID. Now click on Register app.
Step 5: In the next step, Download the GoogleService-Info.plist file and keep it safe, you will need to add this file to the Apps Creator Dashboard later.
Step 6: Skip the next two steps by clicking on "Next".
Step 7: In the last step, click on "Continue to Console" to go back to the Firebase Project.
Step 8: Click on the Cog Wheel icon, on your Project Dashboard page and open your Project Settings.
Step 9: Navigate to Cloud Messaging tab in Project Settings.
You need to grab the Cloud Messaging API key from this page. However, you may find that the Cloud Messaging API (Legacy) is disabled for your account by default. You can enable it by Clicking on the three dots in the right corner and then clicking on "Manage API in Google Cloud Console". This will take you to the Google Cloud Console Dashboard, there you can enable this API.
Once enabled your will find the API Key under Cloud Messaging tab.
Copy this Server API Key, we will need it in the next step.
Step 10: Login to your Apps Creator Dashboard and navigate to Content >> Channels >> Channel Setup >> Apple (iOS). Here, upload your GoogleServices-Info.plist file and paste your Server API Key in the text box (make sure there are no additional spaces at the front or end of the key). Save the form.
Congratulations! You have successfully configured your iOS app on Firebase.