Admob初始化等待时间吗？

Question

当我在Unity中初始化Google Admob并发送横幅广告请求时，大多数情况下都不会显示任何内容。当我在3秒内提出要求时，我就有更多机会。我在想这可能是因为初始化需要时间吗？因此，现在我想知道如何知道何时初始化Admob，或者如何才能最成功地请求横幅广告。这是当前代码：

private BannerView bannerView;


void Start()
{
    #if UNITY_ANDROID
        string appId = ".............REAL ID................."; //ADMOB
    #elif UNITY_IPHONE
        string appId = ".............REAL ID.................";
    #else
        string appId = "unexpected_platform";
    #endif
    MobileAds.Initialize(appId);
    HandleAds();
}

private void HandleAds()
{
    if(....) // some conditions in which to show ads, not relevant
        Invoke("RequestInterstitial",3f); //also not relevant and works very well
    Invoke("RequestBanner",3f); // not works very well
}

public void RequestBanner()
{
    #if UNITY_ANDROID
        string adUnitId = "......Real Id.......";
    #elif UNITY_IPHONE
        string adUnitId = "......Real Id.......";
    #else
        string appId = "unexpected_platform";
    #endif

    bannerView = new BannerView(adUnitId, AdSize.SmartBanner, AdPosition.Bottom);
    bannerView.OnAdLoaded += HandleOnAdLoaded;
    AdRequest request = new AdRequest.Builder().Build();
    bannerView.LoadAd(request);
}

public void HandleOnAdLoaded(object sender, EventArgs args)
{
    bannerView.Show();
}