Originally Posted by
tktravel
My American friend who just traveled to Argentina from U.S. told me that
the airline checks if passengers have the payment receipt before
boarding the plane from the U.S. So it is not an option to show the
second passport at EZE. I wonder if showing the second passport
that is not registered with the itineraries is an option; will the
airplane employee takes it?
It is an option as Argentine immigration aren't concerned which passport you choose to enter with as long as it's valid and affords you the right to enter without a visa or having to pay the fee.
US airline staff on the other hand can get a bit confused when it comes to dealing with people travelling on non US passports.