TrenItalia itself runs as far as Lecce-an eco-friendly town that has a few yrs ago installed a trolleybus system (electric bus, old style, under wires). Use of it is minimal however. That is some 100+ KMs south of Bari-via main town Brindisi.

The rest of the network-with a very meagre service used to be served by FSE=Ferrovie Sud Est (guess what that would mean?) and this has a few yrs ago-due to enormous debts and probably also rampant corruption-gone bankrupt and was forced to be taken over by tr-it. It however has ever since (as far as I could distract from well-informed sources on specific forums) not accepted the passes that tr_It does. In summer only it offers its very own quite cheap pass (that is, at least pre-covid). And normal tickets are not overly expensive for west-Eur standards=one of the reasons it went bankrupt. It runs in the ´heel of the boot´ that IT is commonly compared to. Farthest point is Otranto (cheapest ferry to GR). I´ve been once on it-at least some 5/6 yrs ago, before take-over, and it was effectively only used by screaming studenti. But perhaps angelo dalle IT knows a little more.

That some local networks do not take passes is pretty common also in other parts of Italy and has always been the case. There are also 2-3 other local(not really private) railways also in this part, Calabria-going more inland. As is the case in several other countries.

I see, thanks! We want to go to Otranto, so fair enough, if you can get all the way to Lecce, it's not too bad. Thanks a lot for your reply!