Ok the problem here is that some devices are not able to see the ads, and after some revision on the devices and some discard process I found that the devices with "Limited Ad Tracking" won't show any ads. Other SDKs as iron source allow you to call the ad without IDFA in iOS, as far as I know the IDFA won't be used when "Limited Ad Tracking" is on so I guess Admob uses this as a needed element for requesting ads. I hope someone knows how to request ads when "Limited Ad Tracking" is on. Here is my code:
//MARK: - Request AD
var rewardBasedVideo: GADRewardBasedVideoAd?
func requestAd(){
rewardBasedVideo = GADRewardBasedVideoAd.sharedInstance()
rewardBasedVideo?.delegate = self
rewardBasedVideo?.load(GADRequest(), withAdUnitID: "ca-app-pub-9505104597698750/8748625825")
}
//Show Video (This function is called on a button action)
func showVideo(){
rewardBasedVideo?.present(fromRootViewController: self)
}