Trying to use Alpha with Tri-Planar but not seeing material

Hopefully I’ve properly described the problem. Trying to follow this tutorial https://www.youtube.com/watch?v=5-o38kORqt8 and I’ve just about managed to get an alpha to appear on one of the tri-planar surfaces, but it doesn’t create any object. No idea where I am going wrong, very much a noob.

Please can anyone offer some advice?