Sprite become invisible with Shader

Hi, my name is Víctor and I'm trying to learn a little bit of Sprite Shaders.

By now I have this Shader Graph:
https://gyazo.com/d6228415721216a3b97189501a599e5e

But when I save and apply, Sprite dissapears.
If I change Alpha parameter to 1 it appears a red circle on the screen:
https://gyazo.com/1217ec970bfd8db134f9eb2f98609447

Changing from PBR graph to Unlit Graph it solves the problem but, what's the difference between them ? Shouldnt I use pbr graph to Sprite Shaders ?

Any idea of how can I solve it ?
Thanks in advance.