RSS feed leads to “page not found”

Hello,

I have installed Ultimate Social Media Plus and it works for LinkedIn, Facebook, Whatsapp and Follow by Email. The RSS Feed button opens a new page ending with /feed/, as it should. However, on this page it says: “Not found. Apologies, but the page you requested could not be found. Perhaps searching will help.” Can somebody help to figure out why this is not working properly?

The page I need help with: [log in to see the link]