Unable to make clipping mask with an image file

jungleboogle,

As I (mis)understand it, you will be happier with an Opacity Mask (Transparnecy panel) .

Presuming you wish to have only the wavy lines showing beneath the black angular image parts, have the image on top of the lines, then select both and (Opacit) Mask Make with both Clip and Invert Mask ticked.

So you want to put the lines into the geometric shape?

The geometric shape needs to be a compound path or a text object. Is it?

It also needs to be the top object (Arrange > Bring to front) Is it?