This is the absolutely normal situation that right after generation of the first version of your game you would not see and banners. It happens because there need some time to connect your game to selected AdNetwork. It can take up to 48 hours to start serving banners after you will upload game to Google Play (or any alternative app store).
So please - Generate Game => Upload it to Google Play => Wait 48 hours and only then check if banners are showing. This delay affects only NEW JUST REGISTERED GAME. After creating new version ads will show immediately.
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