How to make a lips image (.png) follow the mouth of the Face Mesh?

How to make a lips image (.png) follow the mouth of the Face Mesh?

I’m using the Studio, I don’t have the pro plan.
So I just created a new Project in the Studio, cloning the (Basic) Face Effects Project that comes with the Stereo Glasses as a .glb. and it has a .png in the Face Mesh.

I changed the Face Mesh texture to my own image, that has a mouth on it. Since it is linked straight to the Face Mesh I though it would automatically start to follow the Face’s mouth. But it didn’t.

What is missing to link the Actual Mesh to the Face ???
In the original project it has a text in the forehead that is “Static”. In my case it is a mouth, so it is “Flexible”. How could I make this link? What is missing??