Recently Google sent the notification to all the Google Publishers about a recent update about declaring authorized seller with ads.txt. This update is an IAB initiative that helps ensure that your digital ad inventory is only sold through sellers (such as AdSense) who you’ve identified as authorized.
How to fix it?
1. Create an ads.txt file with the following code
google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0
(Replace that 0000000000000000 with your publisher ID )
2. Upload this file in the root level of your domain.
If you are using cPanel for accessing your website file the login and upload file from your cPanel or FTP server. Make sure it in your root domain, not in sub-domain or sub-folder.
3. Check www.yourdomain.com/ads.txt to check if you successfully upload the valid file. If is successfully uploaded then you redirect to page like this.
4. Wait for another 24 hours.
5. Do the same with your other sites if you have multiple sites in a single AdSense account.
What is This Warning Actually?
Creating own ads.txt let it’s creators more control over who’s allowed to sell ads on the site and helps prevent counterfeit inventory from being presented to advertisers. It can help buyers identify counterfeit inventory and help to receive more advertiser spend that might have otherwise gone toward that counterfeit inventory.