How to work with JSON Curve Object

I'd like to be able to draw an ellipse by adding two "elliptics arcs", but I struggle to Get the Geometry from a JSON activity:

my JSON matches with the exemple shown there https://developers.arcgis.com/documentation/common-data-types/geometry-objects.htm

here is my JSON , ext1 and ext2 are the origine and extremety of the major axis, and the picked geometry is the center of the ellipse.

={

 "curvePaths":[[  

  [$ext1.result.x,$ext1.result.y],

{"a": [[$ext2.result.x,$ext2.result.y],[$form1.state.geometryPicker1.value.geometry[0].x, $form1.state.geometryPicker1.value.geometry[0].y], 0, 0, Math.sin(50*(Math.PI/180)), 25, 0.5]}

 ]],

spatialReference: {wkid: 102100 , latestWkid: 3857 }

}

The geometry returned from the activity is "undefined".

Attached, my workflow (the number sliders are not yet taken into account)

Any help appreciated !

@Latitude Development? @Stefan Schweigert? @Amanda Frech?