Thank you @wozza - very useful information.
We have been using APRR, now Fulli for many years and never had a problem. We used to live in the North East Metz, Lorraine, and bought a “tourist” tag for the odd trip. Now we live in Les Landes and have kept APRR/FULLI, despite it being based on the East side of France. Today we have the “International” version (France, Spain, Portugal, and Italy) which we have tried in all four countries. It worked well with all the different systems. The monthly fee in France (when used) is 1,70 euros and the other 3 is about 2,40 euros per month (when used).