Missing google_app_id

[psyanite]

Describe the bug
I am no longer able to see ads after I upgraded to AndroidX and now running stable Flutter. :(

I've noticed that we now have 3 AndroidManifes.xml files? I just put the google app id inside the one in src/main. I am also trying to run test ad but is no longer working anymore.
Error:
Missing google_app_id. Firebase Analytics disabled. See https://goo.gl/NAOOOI

Thanks for reading my report, appreciate any help provided.

Android Manifest

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.burntoast.nameme">
    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
         calls FlutterMain.startInitialization(this); in its onCreate method.
         In most cases you can leave this as-is, but you if you want to provide
         additional functionality it is fine to subclass or reimplement
         FlutterApplication and put your custom class here. -->
    <application
        android:name="io.flutter.app.FlutterApplication"
        android:label="NameMe"
        android:icon="@mipmap/ic_launcher">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">
            <!-- This keeps the window background of the activity showing
                 until Flutter renders its first frame. It can be removed if
                 there is no splash screen (such as the default splash screen
                 defined in @style/LaunchTheme). -->
            <meta-data
                    android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
                    android:value="true" />
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <!-- Google Ads Admob configuration -->
        <meta-data
                android:name="com.google.android.gms.ads.APPLICATION_ID"
                android:value="ca-app-pub-6524279756456110~1563270059"/>

    </application>
</manifest>

Flutter run -v

flutter run v.txt

Flutter doctor

[psyanite]

Fixed, missing

apply plugin: 'com.google.gms.google-services'

from /app/build.gradle.

[korenzerah]

It happened to me also.
The reason I missed adding the plugin is that in the firebase_admob README.md, they say to do the steps 1-3.1:

While adding the plugin to the build.gradle file is mentioned in step 3.2.
The README.md should be updated or there is something I didn't understand.