Does anyone know how these function when you don't know they exist and you don't pre-register or have a tag? (We drive in mainland Europe fairly often, so no issue with the usual tolls with tickets and payment booths, well used to those.)
This trip hit a bit of the Sanef toll roads that don't have tickets or payment machines, though. I hadn't pre-registered my car (given that I didn't know they exist!), but I went online and did it as soon as we reached our destination. No fees have landed retrospectively, though.
We came a different route back - presumably this would have registered, but didn't meet any of the 'flux libre' on the route home.
I suppose at least I can demonstrate that I registered on the same day, but not sure what else I can do with it, really?