feed – Debugging problems with WordPress RSS widget?

I’m trying to add an RSS feed to a wordpress site using the RSS widget. When I enter the URL into the RSS widget I get RSS Error: WP HTTP Error: A valid URL was not provided. (or sometimes I get nothing — no error, but no content).

The feed validates successfully using the W3C feed validator.

If I expose the feed on a different site (e.g., grab the feed content with curl, serve it somewhere using a simple http server, and point the rss widget at it), it works just fine.

This leaves me to wonder if the RSS widget is experiencing some failure unrelated to the feed itself…stale DNS? Something else?…but I’m not sure how to diagnose that. This is a hosted wordpress site so the only access I have is via the WP UI. Is there anything I can do to figure out why exactly the RSS widget is failing?

To be clear, this works just fine:

  • curl -o feed.xml https://.../feed.xml
  • darkhttpd . --port 8080
  • ngrok http 8080

…and then point the RSS widget at the ngrok url.

So the same content, fetched from the canonical location, just hosted at a different URL.