Problem: In AdSense panel, there is a prompt telling you that your website is missing ads.txt
Solution: Go to AdSense panel, find and copy your publisher ID (In Account Information), create ads.txt file and contains below information:
google.com, pub-your_publisher_ID, DIRECT, f08c47fec0942fa0
Put ads.txt in the website root folder, and this file must be viewable in public. And wait for a few hours to 1 day, and this will problem will be solved.