Using GoogleMobileAds (SDK: v7.X.X), for Reward Ads.

Rewarded.swift

//MARK: - Rewarded
final class Rewarded: NSObject, ObservableObject, GADRewardedAdDelegate {
    
    @Published var isReady: Bool = false
    private var adUnitID: String = ""
    private var ad:GADRewardedAd?
    private var adFunction: ((Bool) -> ())?
    
    override init() {
        super.init()
    }
    
    func start(adUnitID: String) -> Rewarded {
        self.adUnitID = adUnitID
        self.load()
        self.observe()
        return self
    }
    
    private func load() {
        self.ad = GADRewardedAd(adUnitID: self.adUnitID)
        self.ad!.load(GADRequest())
    }
    
    private func observe() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 30) {
            self.isReady = self.ad != nil ? self.ad!.isReady : false
            self.observe()
        }
    }
    
    func showAd(rewardFunction: @escaping (Bool) -> ()){
        self.adFunction = rewardFunction
        if self.ad!.isReady {
            let root = UIApplication.shared.windows.first?.rootViewController
            self.ad!.present(fromRootViewController: root!, delegate: self)
        } else {
            if self.adFunction != nil {
                self.adFunction.unsafelyUnwrapped(false)
            }
            self.load()
        }
    }
    
    func rewardedAd(_ rewardedAd: GADRewardedAd, userDidEarn reward: GADAdReward) {
        if self.adFunction != nil {
            self.adFunction.unsafelyUnwrapped(true)
        }
        self.load()
    }
    
    func rewardedAdDidDismiss(_ rewardedAd: GADRewardedAd) {
        if self.adFunction != nil {
            self.adFunction.unsafelyUnwrapped(false)
        }
        self.load()
    }
}