Deneb - Add data labels as a layer to Focus + Context - Smooth Histogram Zooming

Hi,

I have a visual set up based on this json in Deneb.

Focus + Context - Smooth Histogram Zooming 

Now I am trying to edit it to suit my needs and ideally when the end user uses the brush I would like data labels to appear on the bottom bar chart to show. Now i would usally add this with a layer but i can't seem to get the code correct.

Is it because of use of vconcat? Im not sure.

Any help appreciated.

TIA

JJ