The brush icons were not working for me.
I tried scaling the png image in GIMPto 512x512 and 80x80.
Help us all to help you.
Please give full screenshots with any questions. With the relevant panels open.
This can be done by Blender itself, via the ‘Window’ menu bar top left-hand side.
On that menu dropdown is ‘save screenshot’.
The reason for this is that we can also see, Blender version and other options/connections
Try to start a new Blender file and import the brush, and see if it is still not working! Just to analyze the problem.