Knife tool wont cut on face

Hi forum.

I’m trying to use the knife tool, so I can make a cut/slice from vertex to vertex and sometimes I cannot make this happen.There is no Ngons so what am I not doing incorrect? or why is Blender not allowing this action to happen?

Thank you.

I guess the vertice you want to cut to is not on that face. It belongs to the face below.
To cut to there you have to activate snap vertices.