Okay, but just out of curiousity...

So SCL-MDZ-AEP, with just a connection in MDZ, (but not a stopover ) would not incur the fee? Simply connecting in MDZ would avoid the fee, as opposed to a direct flight? Why would a foreigner ever not connect first then?

Is it not conceivable that some people on the MDZ-AEP flight would be people just connecting in MDZ (from SCL as a starting point).

And some people on that same flight would just be people flying direct MDZ-AEP (without SCL as a starting point). How do they determine who will pay the fee from the passengers deboarding the same plane.