Trying to apply this Free Eye Texture

TO: This Free Model

I'm trying to follow the instructions:
Navigate to your Eye Material on your avatars head and replace it with the Material provided that was just imported.

But once trying to drag drop it.. the eyes become invisible?..

I'm usually smarter then this, but i'm just having helluva brainfart

Things to note!
I have all the required repo's and all kinds of otherones (modular avatar ect).

i would SUUUPER appreciate some pointers and instructions that would help me out now and into the future! cheers!!!