Get following response from Admob:
This might be caused by no inventory available for that ad unit ID at that time. This is usually unrelated to your implementation if you are able to show ads with our test ad unit ID (Android,
iOS,
Unity). Sometimes this problem will be solved after you released your app and get more traffic.
Advertisers can target specific regions, platforms and user profiles based on business relevance, which can sometimes result in lower availability of Ads for a particular region or user profile. Error code suggests that the implementation is correct, and that the ad request was not filled because of lack of availability of a suitable Ad at that particular instant of time when an ad request was sent from the app. As we cannot manipulate advertiser demand, there are no particular ‘fixes’ for this error. You can cross-check the ad unit implementation to ensure that the ad units are implemented correctly.
In some instances, certain Ad Networks may have limited performance in some regions or for specific formats, in which case the pubs can try using mediation to add other Ad Networks that may potentially perform well.
It might also be due to policy violation which limits your ad serving. Check your AdMob Policy Center and resolve any violation that you have. Please also check your
Children’s Online Privacy Protection Act (COPPA) status as this might impact on your ad serving as well.
If issue persists, please
contact our support team.
Additionally, if you have been asked to submit your APK, or if you have a problem serving Google ads in your Android application, you can complete the
APK submission form.
You can also read more details from our community discussion thread
here.