WordPress sites are INACCESSIBLE on Linked

I continue to get an error message on Linkedin when I try to install my WordPress blog into the application:
The feed URL http://balloffireconsulting.com/blog?feed=rss2 is inaccessible.

And yet my url is valid….. WHY isn’t it being accessible through the Linkedin WordPress app????