How to put a simple banner ad on google play for free

Hi Id like to start monetizing an app I have on google play. Thinking of just showing a banner at the start menu. When looking at unity ads, I can only find tutorials that would show how to put a video ad up which is not what Im looking for. Then checking up admob from google I read that it forces me to create an adword account. And apparently you have to pay with adwords constantly I dont want to advertise myself, only others. Any way of just putting up a banner? Thank you

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using GoogleMobileAds.Api;

private void RequestBanner()
{
    #if UNITY_EDITOR
        string adUnitId = "unused";
    #elif UNITY_ANDROID
        string adUnitId = "INSERT_ANDROID_BANNER_AD_UNIT_ID_HERE";
    #elif UNITY_IPHONE
        string adUnitId = "INSERT_IOS_BANNER_AD_UNIT_ID_HERE";
    #else
        string adUnitId = "unexpected_platform";
    #endif

    // Create a 320x50 banner at the top of the screen.
    BannerView bannerView = new BannerView(adUnitId, AdSize.Banner, AdPosition.Top);
    // Create an empty ad request.
    AdRequest request = new AdRequest.Builder().Build();
    // Load the banner with the request.
    bannerView.LoadAd(request);
}