What is app-ads.txt?
app-ads.txt is a plain text file that lists which ad networks are allowed to sell ads in your app. Advertisers check it to avoid fake inventory. If the file is missing or wrong, networks like AdMob show a warning and may serve fewer ads, which means less money for you.
The line format
Each line has three or four fields separated by commas: the ad network domain, your account ID on that network, the relationship (DIRECT if you have your own account) and an optional certification ID.
google.com, pub-1234567890123456, DIRECT, f08c47fec0942fa0
The most common mistakes
Using the AdMob app ID (ca-app-pub-…~…) instead of the publisher ID (pub-…). Putting the file on a different domain than the one in your store listing. Hosting it in a subfolder instead of the root. Redirecting http to a different domain. After you fix it, AdMob can take up to 24 hours to crawl the file again.
Where do I host it if I have no website?
A free GitHub Pages or Cloudflare Pages site works. Set that address as the developer website in Google Play Console or App Store Connect, then put app-ads.txt at its root.