Common ads.txt mistakes that break monetization
Fix typos, wrong pub IDs, bad formatting, and hosting the file in the wrong place.
1) Putting the file in a subfolder (it must be at /ads.txt).
2) Wrong publisher ID (pub-...) or missing google.com line.
3) Bad formatting: not enough fields, wrong DIRECT/RESELLER spelling, extra commas.
4) Serving as HTML instead of plain text (text/plain is recommended).
5) Using HTTP only when your site supports HTTPS (prefer HTTPS).
Re-check after changes. Crawlers may need a bit of time to update.