PCI-E passthrough: pci-stub/bind says no such device

so im trying to bind my second radeon card to pci-stub, as per instructions for setting up GPU passthrough in here, but once i get to binding the card to pci-stub, it tells me it isnt there. this is what im putting in, and what i get out:
i modified some of the path as some of the ones in the documentation dont seem to exist on my system, however according to my file manager /sys/bus/pci/drivers/pci-stub/bind definately exists. im trying to give my windows vm a HD6450 so i can actually use it for things, but its proving difficult thus far.