I'm trying to add a button widget in one of our test sites, created using the Zet-CLI Tool.

When I host the Widget externally it runs fine, making a call to a UK Government API and downloading some json and displaying a table of data.

If I try to host internally, using zet pack to create the upload file, the window pops open and it is empty. When I look in the console I see "ReferenceError:  ZPWidget is not defined". Have I missed something in the Widget set up?