Inability to add blog to icerocket

I do not see this in the archives, so I though to ask here:
https://www.icerocket.com/ allows one to add via this page: https://www.icerocket.com/c?p=addblog for which I enter in my blog url: https://www.formulateaffinity.com/ and get:

IceRocket was unable to find XML feed for this URL.

I should note, I get this with any WP blog I point at it, so I wonder what the solution is.