Chartboost with Swift - Interstitial: prefetch if NOT complete. wait... but no ad?

I am trying to integrate Chartboost ads in Swift into my project and have followed the tutorial verbatim:

https://answers.chartboost.com/hc/en-us/articles/205853276

Everything is imported and in App delegate I have:

Chartboost.startWithAppId(//stuff)
        Chartboost.setShouldRequestInterstitialsInFirstSession(false)
        Chartboost.cacheMoreApps(CBLocationHomeScreen)

//Chartboost

class func showChartboostAds()
{
    Chartboost.showInterstitial(CBLocationHomeScreen);
}

func didFailToLoadInterstitial(location :String!, withError error: CBLoadError)
{

}

func didDismissInterstitial(location :String! )
{
    if(location == CBLocationHomeScreen)
    {
        Chartboost.cacheInterstitial(CBLocationMainMenu)
    }
    else if(location == CBLocationMainMenu)
    {
        Chartboost.cacheInterstitial(CBLocationGameOver)
    }
    else if(location == CBLocationGameOver)
    {
        Chartboost.cacheInterstitial(CBLocationLevelComplete)
    }
    else if(location == CBLocationLevelComplete)
    {
        Chartboost.cacheInterstitial(CBLocationHomeScreen)
    }
}

Then in my main view controlleR:

AppDelegate.showChartboostAds()

I have my app in test mode in the dashboard and am running on a real device but I just get Interstitial: prefetch if NOT complete. wait... in the console.

Why won't it show any ads?

I think you're trying to show the AD to quickly. Try delaying the AD, that solved it for me.