Thomas,
Thank you for reaching out to me via the ArcGIS Hub Questions thread above. I have since resolved my issue, and it was caused by the Spatial reference used not being a standard WKID. In fact the Spatial reference used was a customized one base on WKID 27700. Because it did not match WKID exactly, Hub could not find the WKID definition required for the API to initialize for the download. When I disabled local reference, the API enabled and +-