We recently updated the Incorrect mapping optimization status to Can’t retrieve data. This updated status allows us to describe more possible causes of this optimization issue. If you encounter this status message, check the following:
Ad unit mapping
Confirm that your ad unit mapping details are correct. The mapping details in your AdMob account must match the mapping details in your third-party ad source account. Additionally, your ad units must exist in the third-party ad source and be able to serve ads. Learn more about the required ad unit configuration details by ad network.
Confirm your ad source credentials are correct for this ad source and app. Learn more about the required optimization credentials by ad network.
Additionally, check that the credentials for your third-party ad source have permission to access reporting data. This is handled in your third-party ad source account.
Confirm this ad source instance is receiving requests and reporting impressions. If requests or impressions are zero, check your SDK implementation to ensure ad requests are reaching AdMob for third-party ad sources.
You can use the Mediation Test Suite to test whether you have correctly configured your app and ad units to be able to display ads from third-party networks through mediation.