How can one create shapes in PowerPoint with Javascript for automation?

I am trying to create a new shape in PowerPoint with Javascript for automation on Mac like this:

var ppt = Application('Microsoft PowerPoint');
ppt.Shape().make({ autoShapeType: "autoshape rounded rectangle", width: 100, height: 100})

this generates an error:

execution error: Error on line 2: Error: Parameter error. (-50)

since the JAX documentation is a bit terse, and there is nothing specifically on PowerPoint, does anyone have an idea of how to fix this and how to generate/undrstand/bootstrap some kind of documentation on MS Office javascript automation on Mac