Self reference doesnt match document location

This error is due to the redirect from http to https in Rails app, because SSL is forced. Change  http to https to avoid redirection in the tag as follows:

xml.tag!("atom:link",  "href"=>"https://rubyplus.com/episodes.rss", "rel"=>"self", "type"=>"application/rss+xml") 

This way, the feed validator will not get confused due to the redirect.