Zbrush Displacement Maps not working?

[RealityFox]

I've looked through the manual on how to use displacement maps, it just seems to say you plug the texture into the Displacement Texture node and such. The thing is, that it works fine when I use Xnormal (well not really, I think my displacement map may have been funky, I got black outlines for some reason) but when I use a displacement map from Zbrush it doesn't do anything. Anyone can tell me why? Octane grabs the red channel automatically so I presume it should work with Zbrush.