HTTP Headers Warning Public_HTML Not Found

Thank you for such a great plugin you built.

I have used your HTTP Header plugin and it works for most of my websites, except the last one which is https://www.markonemfg.com/.

The plugin keep warns me about the “The following file was not found. Please make sure the file exists and has write permissions: /home/markonem/public_html/”

What should I do from this point?

I use https://webpagetest.org/ to test the header, but it seems like the my setting didn’t applied yet.