title: AdMob interstitial error "Request Error: No ad to show"
body: <p>I'm developing an iOS application using Swift2 and Xcode7. I'm trying to implement AdMob but it doesn't display my interstitial ad.</p>
  
  <pre><code>override func viewDidLoad() {
      super.viewDidLoad()
  
      _interstitial = createAndLoadInterstitial()
  }
  
  func createAndLoadInterstitial()-&gt;GADInterstitial {
      let interstitial = GADInterstitial(adUnitID: "interstitial_ID")
      let gadRequest:GADRequest = GADRequest()
      gadRequest.testDevices = ["test device id"]
      interstitial.delegate = self
      interstitial?.loadRequest(gadRequest)
  
      return interstitial!
  }
  
  func interstitialDidReceiveAd(ad: GADInterstitial!) {
      _interstitial?.presentFromRootViewController(self)
  }
  
  func interstitial(ad: GADInterstitial!, didFailToReceiveAdWithError error: GADRequestError!) {
      print(error.localizedDescription)
  }
  
  func interstitialDidDismissScreen(ad: GADInterstitial!) {
      _interstitial = createAndLoadInterstitial()
  }
  </code></pre>
  
  <p>I receive this error:</p>
  
  <blockquote>
    <p>Request Error: No ad to show.</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/mMVQH.png" rel="noreferrer"><img src="https://i.stack.imgur.com/mMVQH.png" alt="enter image description here"></a></p>