Hummingbird uptime monitoring error

When I try to enable uptime monitoring it gives me this error:
"Your domain does not appear to be publicly accessible on the Internet."

What I found debugging on my own:
- The site is 'publicly available on the internet' (or at least you can type it in a browser and it shows up)
- Under WordPress General Settings, the site IS allowing access to search engines (not hiding)
- Is Hummingbird having trouble because it is a multisite installation?