Andrea,
I'm not the developer of jsonstat.py so I can't answer specifically on issues related to this Python library.
That said, if you look at the front page of
json-stat.org you'll notice that Istat is crossed out. In the very beginning JSON-stat was a project of Vincenzo Patruno (Istat) and myself. Vincenzo developed an API that allowed to retrieve Istat's datasets in the JSON-stat format (v.1). Thanks to that effort, Istat was the first NSI to serve its datasets in the JSON-stat format (and, at the time, I think that was the only public API at Istat).
Unfortunately, after many years working perfectly, Istat discontinued such effort some years ago.
X.