title: Why isn't my app showing AdMob ads?
body: <p>I have this Android application that has ads but they are not showing.
  In my LogCat it says:</p>
  
  <p><code>onFailedToReceiveAd(Ad request successful, but no ad returned due to lack of ad inventory)</code></p>
  
  <p>Does anyone have an idea why aren't they showing? thanks</p>