I'm trying to create a shortlist story map using data in an existing web map as the data source as described (very briefly) here in step 1.
Story Map Shortlist Tutorial | Story Maps
I have my web map with a layer using the correct schema, and containing some sample data.
http://delaware.maps.arcgis.com/home/webmap/viewer.html?webmap=6b4f15b068f84086adb86145cf05f099
But when I try to create a new web app, story map shortlist is not an option in the template gallery.

I've gone several ESRI and non-ESRI sets of instructions for this and can't figure out what's going wrong. Any ideas? Thanks.