Transparent material

[ViaCognita]

I’m newbie and I’m trying to create a mask to Emissive Color.

This is my material:

I have created a Blueprint actor with a MaterialBillboard using that material (I’m not using a material instance). But, as you can see, the material it isn’t transparent:

Attached it is the image that I’m using.

How can I show only the red part of the image without the black background?

[NasteX]

Pick the white pin from the black and white texture and connect it to opacity.