Thanks @Jonathan5.
Have you tried W3C Feed Validation Service, for Atom and RSS ?
I get a similar message.
It looks like this is a web page, not a feed. I looked for a feed associated with this page, but couldn’t find one. Please enter the address of your feed to validate.
Any advice on how to troubleshoot, as I appear to be doing what’s explained at Enabling RSS feed on Discourse setup - #8 by codinghorror?