Originally Posted by
xliioper
There are regional limitations to combining discount J fares in an open-jaw construction and you are almost certainly not meeting those, so the $10,300 C fares are likely all you will ever get from Delta. There are roundtrip Z fares available to PPT and SCL from JFK in the $4000 - $4500 region. They just can't be combined together an open jaw. The C fares only require that the jaw distance be shorter than the two other legs.
This would mean that the AmEx fare is invalid and shouldn't ticket. YMMV of course, but it's unlikely that a Z fare would work for this combination of flights.
Also, I'm not sure that the IAP covers open jaw tickets rather than just RTs. Check the T&C to be sure.