How do I set up an ads.txt file for Blogger?

The purpose of implement this ads.text is to avoid any unauthorised sellers to misuse your ads space. In order for them to bid the ads  space is they must follow the proper way.

This is also benefit you in the future. This will help to protect your earning and avoid unauthorised seller to bid your ads space without your permission. 

How to set up an ads.txt file for Blogger? - this YouTube video is from WebbyFan.com 

create an ads.txt file on your sites, here's what you need to do: 1. Sign in to your AdSense account. 2. In the alert on your homepage, click Fix now. 3. Click the Down arrow to open the "Create an ads.txt file for..." message. 4. Click Download. Your ads.txt file is automatically downloaded. 5. Upload the file to the root level domain of your site (for example, https://example.com/ads.txt). Root levels are one level down from what’s listed in the public suffix list. For example, "google.co.uk" is a root domain of "co.uk" but "maps.google.co.uk" is not. See the IAB ads.txt specification. To add your publisher ID to an ads.txt file 1. Sign in to your AdSense account. 2. In the alert on your homepage, click Fix now. 3. Click the Down arrow to open the "Add your publisher ID to these ads.txt files" message. 4. Click Copy. 5. Paste the line into each of your ads.txt files. Your ads.txt file should now look like this, where pub-0000000000000000 is your own publisher ID:

google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0