Are there any TER discounts which can be used even for cross region travel? To take a concrete example, what about a Lyon → Marseille train, which goes from Rhône-Alpes to Provence-Alpes-Côte d'Azur (PACA)? There are separate discounts both in Rhône-Alpes and in PACA, but what about travel from one to the other?
I am asking here because I found even the regional discounts difficult to discover, and they turned out to be usable only when buying tickets from the ticket office (not from the ticket machine, and not from voyages-sncf.com).
I am looking for discounts specifically for TER (not TGV or other high-speed trains), and only for those which do not require the payment of a one-time fee (e.g. purchase of a card) and which have no age restrictions.