the hardware is already configured on the recording server
The simplest explanation is that you cannot add the same device twice on the same recording server, can you please double-check whether this is what happens?
NOTE. You cannot add the same device twice using the same IP address and port, but be also aware that if you for some reason have given that device a new address it will be detected as being the same device because XProtect will use the MAC to detect whether it is the same device.
how to remove the existing mac address?
we are using a windows server 2012
it was removed for service a long time ago and we get back it last month.
now we cannot add the camera on the same server.
When you see the message, this means that you had already added the device and you have it on your VMS. The device might be disable now but you will need to find it and remove it. If still does not work properly then please ask again in the support community, you should get better help from the partners using the support community.