Ads.txt is IAB initiative to identify Authorized Digital Sellers of online inventory.

It is part of an effort to increase transparency and legitimize programmatic buys and combat unauthorized selling of publisher inventory.

NOT IMPLEMENTING ADS.TXT ON THE SITE MAY AFFECT AD PERFORMANCE.

Implementation is easy, and is a text file that is hosted on a publishers web server posted by the webmaster.

You can read more about Ads.txt here: https://iabtechlab.com/ads-txt/