No output on author comment feed

Landed correctly to this page after adding "Recent Global Author Comments Feed" tag to previous post.
My question is
Followed installation instruction and uploaded php file "Recent Global Author Comments Feed" to /wp-content and tried to access feed but it giving error report.

then tried

After installing plugin "recent-global-author-comments-feed-1.0.2.zip" via wordpress upload panel. I tried to access feed but it giving error report. I tried with and without network activation. comment indexer installed beforehand. Rest of the pages uploading correctly
Screenshot attached. any feedback would be appreciated