I'm testing in local a feed generated from a RESTful API, and I have problems with Akregator because it didn't send in accepts header the mime type 'application/rss+xml' to know the server what format is the best for that request. Akregator prefer 'text/html' over other mime type, but when it receive the index page in HTML it doesn't understand it as a feed.

Headers sent by Akregator:
req_headers: [
  {"host", "localhost:4000"},
  {"connection", "keep-alive"},
  {"user-agent", "Akregator/5.4.3; syndication"},
  {"if-modified-since", "Thu, 01 Jan 1970 00:00:00 GMT"},
  {"accept", "text/html, text/*;q=0.9, image/jpeg;q=0.9, image/png;q=0.9, image/*;q=0.9, */*;q=0.8"},
  {"accept-encoding", "gzip, deflate, x-gzip, x-deflate"},
  {"accept-charset", "utf-8,*;q=0.5"},
  {"accept-language", "en-US,en;q=0.9"}
]

I think it's not difficult add to the accepts header 'application/rss+xml' with priority over 'text/html' when it dowload the feed.