Display AdMob Reward ads and interstitial Ads in Cocos2d by using Objective C

I have been trying to display reward ads or interstitial ads in cocos2d but no success. For interstitial I am using the following code

- (void)createAndLoadInterstitial {
    _interstitial = [[GADInterstitial alloc] initWithAdUnitID:@"ID"];
    _interstitial.delegate = self;
    [_interstitial loadRequest:[GADRequest request]];
}
/// Tells the delegate an ad request succeeded.
- (void)interstitialDidReceiveAd:(GADInterstitial *)ad {
    NSLog(@"interstitialDidReceiveAd");
    if (_interstitial.isReady) {
        //[_interstitial presentFromRootViewController:[CCDirector sharedDirector]];
        [_interstitial presentFromRootViewController:self];
    } else {
        NSLog(@"Ad wasn't ready");
    }
    
}
/// Tells the delegate an ad request failed.
- (void)interstitial:(GADInterstitial *)addidFailToReceiveAdWithError:(GADRequestError *)error {
    NSLog(@"interstitial:didFailToReceiveAdWithError: %@", [error localizedDescription]);
    [self displayBannerAd];
}
/// Tells the delegate that an interstitial will be presented.
- (void)interstitialWillPresentScreen:(GADInterstitial *)ad {
    NSLog(@"interstitialWillPresentScreen");
}
/// Tells the delegate the interstitial is to be animated off the screen.
- (void)interstitialWillDismissScreen:(GADInterstitial *)ad {
    NSLog(@"interstitialWillDismissScreen");
}
/// Tells the delegate the interstitial had been animated off the screen.
- (void)interstitialDidDismissScreen:(GADInterstitial *)ad {
    NSLog(@"interstitialDidDismissScreen");
}
/// Tells the delegate that a user click will open another app
/// (such as the App Store), backgrounding the current app.
- (void)interstitialWillLeaveApplication:(GADInterstitial *)ad {
    NSLog(@"interstitialWillLeaveApplication");
}

For Reward Ads I am using the following Code

- (void)display_reward_ad{
    [GADRewardBasedVideoAd sharedInstance].delegate = self;
    [[GADRewardBasedVideoAd sharedInstance] loadRequest:[GADRequest request] withAdUnitID:@"ID"];
}
- (void)rewardBasedVideoAd:(GADRewardBasedVideoAd *)rewardBasedVideoAd didRewardUserWithReward:(GADAdReward *)reward {
    NSString *rewardMessage = [NSString stringWithFormat:@"Reward received with currency %@ , amount %lf", reward.type, [reward.amount doubleValue]];
    NSLog(@"%@,",rewardMessage);
}
- (void)rewardBasedVideoAdDidReceiveAd:(GADRewardBasedVideoAd *)rewardBasedVideoAd {
    NSLog(@"Reward based video ad is received.");
    if ([[GADRewardBasedVideoAd sharedInstance] isReady]) {
        //[[GADRewardBasedVideoAd sharedInstance] presentFromRootViewController:[CCDirector sharedDirector]];

        UIView  *myView = [[UIView alloc] init];
        [[GADRewardBasedVideoAd sharedInstance] presentFromRootViewController:myView];
        [[[CCDirector sharedDirector] openGLView] addSubview:[GADRewardBasedVideoAd sharedInstance]];
    }
}
- (void)rewardBasedVideoAdDidOpen:(GADRewardBasedVideoAd *)rewardBasedVideoAd {
    NSLog(@"Opened reward based video ad.");
}
- (void)rewardBasedVideoAdDidStartPlaying:(GADRewardBasedVideoAd *)rewardBasedVideoAd {
    NSLog(@"Reward based video ad started playing.");
}
- (void)rewardBasedVideoAdDidClose:(GADRewardBasedVideoAd *)rewardBasedVideoAd {
    NSLog(@"Reward based video ad is closed.");
}
- (void)rewardBasedVideoAdWillLeaveApplication:(GADRewardBasedVideoAd *)rewardBasedVideoAd {
    NSLog(@"Reward based video ad will leave application.");
}
- (void)rewardBasedVideoAd:(GADRewardBasedVideoAd *)rewardBasedVideoAd didFailToLoadWithError:(NSError *)error {
    NSLog(@"Reward based video ad failed to load.");
}

What am I doing wrong? I have tried the above code in apps and it works but it's not working in Cocos2d. I am displaying Banner ads without any problem.

UIViewController* rootViewController = [[UIApplication sharedApplication]delegate] window] rootViewController]];
[[GADRewardBasedVideoAd sharedInstance] presentFromRootViewController:rootViewController];