Please keep in mind that the availability of ads is not guaranteed. This is why we provide methods to first check if ads are ready and can be shown. Users are limited to 25 ads per day per app. They are also limited to seeing the same ad only once per hour. For most of Europe and North America, this typically isn't an issue. In countries where fill may be limited, the effects of this can be more obvious. For instance, if there are only 12 ad campaigns available in a user's country, they will only be able to see up to 12 ad campaigns per hour. In any case, if the user exhausts their daily limit of 25 ads, they won't see any more ads until the next day. During development, it's recommended that you enable test mode to ensure you will always have test ads available.