mask - Trying to get pattern into specific shape - GIMP

I am trying to get a specific pattern into a shape with GIMP using layer masks. But i cannot make it work, either the layer mask is grayscale for some reason or i cant get the pattern to show.

This is the shape i am trying to fit the pattern into

And this is the texture i want, but only in the shape above

I assume it has something to do with getting a transparent layer made and then making adding the texture as a layer mask or something. Can anyone help?

Answer

• On the green layer: Layer>Transparency>Alpha to selection


• Hide the green layer


• On the other layer: Layer>Mask>Add layer mask and initialize to selection.