If you’ve modified your site’s robots.txt file to disallow the content crawler from indexing your pages, then we can't serve Google ads on these pages.
To update your robots.txt file to grant our crawler access to your pages, remove the following two lines of text from your robots.txt file:
User-agent: Mediapartners-Google
Disallow: /
This change allows our crawler to index the content of your site and provide you with Google ads.
Note: Any changes that you make to your robots.txt file may not be reflected in our index until our crawlers attempt to visit your site again.