アプリ起動広告を実装するUnity+Admob

using UnityEngine;
using GoogleMobileAds.Api;
using System;
using GoogleMobileAds.Common;
using Unity.Services.RemoteConfig;

public class AdmobUnitOpen : AdmobUnitBase
{
    private DateTime expireTime;
    private AppOpenAd appOpenAd;
    [SerializeField] private string KEY_IntervalSeconds = "openad_interval_seconds";
    private int intervalSeconds = 60 * 60 * 4;  // 4時間

    public bool IsAdAvailable
    {
        get
        {
            return appOpenAd != null
                   && appOpenAd.CanShowAd()
                   && DateTime.Now < expireTime;
        }
    }

    protected override void Initialize()
    {
        // ここでエラーが出る場合は、AdmobUnitBase.csのUseRemoteConfigプロパティを追加してください
        // public bool UseRemoteConfig => useRemoteConfig;
        if (UseRemoteConfig)
        {
            intervalSeconds = RemoteConfigService.Instance.appConfig.GetInt(KEY_IntervalSeconds);
        }
        LoadAppOpenAd();
    }

    public void LoadAppOpenAd()
    {
        if (appOpenAd != null)
        {
            appOpenAd.Destroy();
            appOpenAd = null;
        }

        var adRequest = new AdRequest();

        AppOpenAd.Load(UnitID, adRequest,
            (AppOpenAd ad, LoadAdError error) =>
            {
                if (error != null || ad == null)
                {
                    Debug.LogError("app open ad failed to load an ad " +
                                   "with error : " + error);
                    return;
                }
                Debug.Log("App open ad loaded with response : "
                          + ad.GetResponseInfo());
                // 今からintervalSeconds秒後にexpireTimeを設定(これ以降なら広告を表示してもいいよ)
                expireTime = DateTime.Now + TimeSpan.FromSeconds(intervalSeconds);

                appOpenAd = ad;
                RegisterEventHandlers(ad);
            });
    }

    private void RegisterEventHandlers(AppOpenAd ad)
    {
        // Raised when the ad is estimated to have earned money.
        ad.OnAdPaid += (AdValue adValue) =>
        {
            Debug.Log(String.Format("App open ad paid {0} {1}.",
                adValue.Value,
                adValue.CurrencyCode));
        };
        // Raised when an impression is recorded for an ad.
        ad.OnAdImpressionRecorded += () =>
        {
            Debug.Log("App open ad recorded an impression.");
        };
        // Raised when a click is recorded for an ad.
        ad.OnAdClicked += () =>
        {
            Debug.Log("App open ad was clicked.");
        };
        // Raised when an ad opened full screen content.
        ad.OnAdFullScreenContentOpened += () =>
        {
            Debug.Log("App open ad full screen content opened.");
        };
        // Raised when the ad closed full screen content.
        ad.OnAdFullScreenContentClosed += () =>
        {
            Debug.Log("App open ad full screen content closed.");
            LoadAppOpenAd();
        };
        // Raised when the ad failed to open full screen content.
        ad.OnAdFullScreenContentFailed += (AdError error) =>
        {
            Debug.LogError("App open ad failed to open full screen content " +
                           "with error : " + error);
            LoadAppOpenAd();
        };
    }

    public void ShowOpenAd()
    {
        if (IsAdAvailable)
        {
            appOpenAd.Show();
        }
        else
        {
            Debug.Log("App open ad is not ready yet.");
        }
    }

    private void OnApplicationPause(bool pauseStatus)
    {
        if (!pauseStatus)
        {
            ShowOpenAd();
        }
    }
}