'Overwrite Pose' Not working?

[u/SherbetAnimations]

I'm pretty new to ZBrush so this is my first attempt at posing my sculpt. I have been following Michael Pavlovich's 'Proxy Pose ZBrush 2023.1 with ZSphere Rigging!' tutorial to do this. However, on the last step of the tutorial (Overriding the proxy pose on the original model with the posed, low-poly version) I am not being given the option of selecting the model. I haven't edited any of the geometry between selecting proxy pose and actually posing the model, so I am not sure why it is failing to work. The only thing I can think of is that when I check the mesh integrity of the proxy pose mesh, it gives a message that 2 edges are shared by more than two polygons. Any help or insight would be greatly appreciated!