AdMob Problems

Ok so the ads in my game doesn't work so I made a project with only buttons to show the ads and AdMob plugin.
I am using this code for the ads.

Here is my AndroidManifest.xml located in Assets/Plugins/Android/GoogleMobileAdsPlugin:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.google.unity.ads" android:versionName="1.0" android:versionCode="1">
<application>
<activity android:name="com.unity3d.player.UnityPlayerNativeActivity" android:label="@String/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<meta-data android:name="unityplayer.UnityActivity" android:value="true" />
<meta-data android:name="unityplayer.ForwardNativeEventsToDalvik" android:value="true" />
</activity>
<meta-data android:name="com.google.android.gms.ads.APPLICATION_ID" android:value="ca-app-pub-will_not_post_app_id_here" />
</application>
</manifest>

When I try to build using this, it says @String/app_name not found in AndroidManifest.xml.