The first RSS feed URL address is incorrect, please check that you have a correct RSS feed URL.
If you copy paste the one you gave in Google chrome it shows the following error :
Thank you for your reply. You can check the URL online as we did here : https://validator.w3.org/feed/check.cgi?url=https://www.woudrichem.net/nieuws-woudrichem.rss
As you can see it reports different errors and investigating further we scheduled a Layout with this RSS feed in a test CMS only to find in the Log the error Unable to get feed: cURL error 52: Empty reply from server (see http://curl.haxx.se/libcurl/c/libcurl-errors.html) . This indicates that the server has some configuration setup preventing things other than web browsers to use this RSS feed, and that’s almost certainly the root cause, validation errors aside. We’d recommend if you can to contact the server admin and explain what software you want to use to display the feed to
see if they would be more flexible in their set up eventually. Good luck!