What does zone 2/1 mean in FGC fares and when does each zone apply?

❓ What does zone 2/1 mean in FGC fares?
A journey classified as zone 2/1 means that:

🚆 If you travel only with FGC, it is considered a 1-zone fare between these stations.
🔄 If you transfer to another operator or use a ticket with an unlimited number of journeys (such as T-usual, T-jove, or T-dia), the 2-zone fare applies.