Hi Mateus,
Thank you for reaching out to us.
If you have an app-ads.txt file already set up for your app, kindly ensure that it has a “pub-xxxxxxxxxx” entry that matches the “ca-app-pub-xxxxxxxxxx” section of your app's ad unit ID/s. Otherwise, you may still perform testing by instead assigning your device as a test device, in order to be able to test your real ad unit ID/s.
If the issue persists despite the above, could you then kindly provide the details below (via Reply privately to author) so that I can further investigate the issue?
Regards,
Ziv Yves Sanchez
Mobile Ads SDK Team