Network Not Enabled

Hello everyone, I have been trying to fix this error for weeks and no hope. Please help!
I'm trying to run Admob network on Android and it seems that everything is working well except for the "Enable" part

Note: This is maybe the problem because I don't know where to add this line.. if it's in the AndroidManifest or PTAdheyzapBridge.. please specify in which line should I add the code..

1. import com.heyzap.sdk.ads.HeyzapAds;
2. Activity activity =this;// must be an Activity
3. // Your Publisher ID is: ****************************
4. HeyzapAds.start("***********************", activity);