Follow these steps to create and implement ads.txt file:
1. Open text editor on your computer (the extension of the file should be .txt)
2. Enter the information related to ad servers your demand partners you along with the type of relations with your publisher:
a) Advertising system domain that the traffic is passing through.
b) Seller account ID (channel ID on the platform) that identifies a specific publisher inside your account on the Ad Server.
c) Type of Account that describes your relationship with the publisher. If you are adding your demand partners here, the type of relations will be RESELLER since they are the next link in a chain of programmatic buyers. DIRECT type of relationship with the publisher should be added only if you use Domain White Labeling and work with direct publishers.
d) Certification authority ID represents the TAG (Trustworthy Accountability Group). Some Ad Servers do not have or do not provide their certification authority ID. For example, AppNexus ads.txt line doesn't include certification authority ID as it is shown in the screenshot above.
3. Save the text file on your computer with the name ads.txt.