I'm having the same challenge in adding a Dahua PTZ camera to Hikvision NVR. I can access the camera by connecting it directly to my router with an external power connection. I have identified the IP Address I need to use which is 192.186.254.9...But Dahua config page requires a default gateway address and complains since my network is 192.168.1.1
I have this Dahua PTZ (DH-SD22A204TN-GNI) with all of my other cameras being Hikvision. I followed your instructions and changed my PC IP address so I could set the camera IP address and default gateway for connection to the NVR poe. I can see the camera from the NVR's camera management GUI. The camera IP Address is 192.168.254.9. Default Gateway is 192.168.254.1. Management Port is default 37777. I cannot port forward this port. (I didnt think this was an issue at this point.) I set the adding method to ONVIF. The status of this camera now is unknown error. I don't know how to create a custom protocol if that is what I need to do so please walk me thru that if so. Thanks for any help.
Those are the same kind of problems I'm running into. Unknown error, network unreachable, IP camera does not exist, etc!