Feeder (Android RSS app) and RSS URL

I'm a RSS noob.

I wanted to set up an RSS feed in the Feeder app (Android). But it won't show me any posts.

For example, the RSS link is: https://spin3.sos112.si/javno/ODApi/true (accidents in Slovenia).
If I open this link in Firefox, it downloads the file with the posts. I noticed that downloaded file doesn't have an extension, but I can open it and see posts. In Feeder, which is designed for RSS, nothing happens. No posts appear. Any ideas?