If you're getting an error adding the camera by Onvif, then the inability to connect via Onvif is the first issue to worry about. Is the auto-discovered camera added as "Onvif camera" or is it "Generic Camera" ?
When you add an Onvif camera manually, you're supposed to put only the IP address into the text box, as indicated by the prompt in the box you should see before you type anything, i.e. assuming you set the type to Onvif first.
So, try putting in just the IP address and see if you're able to add the camera first. If you are, it's possible that the camera uses one of the different PTZ modes that we don't support. (We actually don't officially claim to support Onvif PTZ functionality, although we do support some common PTZ modes that cover many Onvif cameras.)
If you get an error even after putting in just the IP address, use "Report Bug" from the hub settings shortly afterwards, and we'll see if there's anything useful getting logged.