The registration was fine.
Some hosts have two or more IP's. When FlexHub connects to the webserver to send statistics, the IP that isn't linked to the DNS can be used for that http traffic. The statistics are then ignored by the webserver because it can't be sure the statistics are from the right hub.
To solve it I've added the second IP for your hub as allowed address. If that's a dynamic IP, it's best to make a different DNS address for it, and let me know, so I can add that one instead of the IP.