Data Driven Material Switcher

Currently trying to develop a system in which the UI populates itself with materials from a data table. These buttons should then switch an object to that material. I have been following the following guide:

However I just can’t seem to get it to work. The current error I’m facing is that the bind event can’t read property of the main widget variable. Please see screenshots below, any advice is much appreciated. I have limited experience with unreal and despite all my efforts I just can’t get this working!