Interstitial ads is not showing

Hi, I'm trying to make admobs interstitial ads work. This is the script that calls it, and when it calls GoogleMobilAdsDemoScript.Instance.ShowInterstitial(); the debug.Logerror says "Worked" which means that the Interstitial is loaded. So why doesn't it show the ad on my phone. everything is correct when i play it in Unity. I'm stuck, so any help and all help is very appreciated. Thanks in advance! :) This is the ShowInterstitial; from the GoogleMobilAdsDemoScript. That I call from another script.