This is a difficult question to answer as there could be many causes, but here's what we recommend, in the following order:
- Go to https://validator.w3.org and copy/paste the URL of your RSS feed to test it. This will let you know immediately whether you have a valid feed. If you do, then continue to 2 below. If you do not, then there is nothing you or we can do about it, except to contact the blog directly and ask them to fix it. Feel free to cc: firstname.lastname@example.org so we can help discuss with them.
- If you have confirmed that the feed is indeed valid, then it's possible our RSS auto-detector is getting confused by something. At this point, you should try a few variations of the feed. Suppose the blog you're trying to feed is located at http://rssfeed.com. First, try to add the URL http://rssfeed.com/feed or http://rssfeed.com/rss. Alternatively, try to navigate directly to the URL of the blog itself, then copy/paste that URL, typically something like http://blog.rssfeed.com or http://rssfeed.com/blog.
- If none of those works, then definitely reach out to us and we'll see what we can do.