The URL in the get call that the hub uses to verify the subscriber is incorrect according to the standard. This is what is should be: http://localhost:1337/?hub.challenge=cab1e01cd13646e5a787e7b2d5d860e1&hub.callback=http%3a%2f%2flocalhost%3a1337%2f&hub.mode=subscribe&hub.topic=5000-2&hub.events=System.String%5b%5d Also, the link for http://localhost:5001/client actually opens http://localhost:50001/client.