How to use GADRewardBasedVideoAd

I want to add reward ads in my application, when user watch the ads video i will give him a reward

what i try to do is something like this in viewdidload i initialize like this :

 let rewardedVideo : GADRewardBasedVideoAd =    
  GADRewardBasedVideoAd.sharedInstance()
    rewardedVideo.delegate = self
    let request2 : GADRequest = GADRequest()
    request.testDevices = [kGADSimulatorID, "id_device"]
    rewardedVideo.load(request2, withAdUnitID: "id reward video from admob")

and later in the application when user decide to play video ads i check this :

 if GADRewardBasedVideoAd.sharedInstance().isReady {

  GADRewardBasedVideoAd.sharedInstance().present(fromRootViewController: self)
        }

the problem is GADRewardBasedVideoAd.sharedInstance().isReady is alway no ready

how can i resolve this problem please ?

any help will be appreciated

___________________Edit

I added this

   func rewardBasedVideoAd(_ rewardBasedVideoAd:  GADRewardBasedVideoAd, didFailToLoadWithError error: Error?) {
    print("error \(error)")
}

and i can see error : Request Error: No ad to show

i don't know may be i miss a configuration

--------------Edit

Solution i used:

like @Daniel Storm suggested, i have to configure third party ad networks for GADRewardBasedVideoAd but when i tried to connect AdColony and Applovin to admob its give me error, somehow adapter it s not connected correcety, i finally choise to integrate chartboost independally of admob, so now i have chartboost for resward video and and admob for banner and intertitiel

i add chartboost like this :

       Chartboost.start(withAppId: "appid configurad in https://dashboard.chartboost.com", appSignature: "signature in the same site", delegate: self)
       Chartboost.cacheRewardedVideo(CBLocationMainMenu)


      if(Chartboost.hasRewardedVideo(CBLocationMainMenu)){


            Chartboost.showRewardedVideo(CBLocationMainMenu)

You have to setup and use third party ad networks for GADRewardBasedVideoAd on AdMob.com.

From Rewarded Video: Publishers Get Started:

Rewarded ads are only available from third-party networks that you've selected for mediation.