Issues with RSS output

Hi there, I am trying to set up the RSS output for my blog to link it to other area's. When I test the RSS link by clicking on the symbols on the blog page it opens up into what looks like a good stream however when I try it on feedburner or flipboard I get told the RSS format is invalid. I have tried using the RSS link in the back end & also by copying the code from the front end but neither work when entered to feedburner or flipboard.

Flipboard RSS requirements https://about.flipboard.com/rss-spec/