Argentina’s reciprocity fee, currently US$160 for US citizens for 10 years, US$75 for Canadian citizens per visit, and $US100 for Australian nationals for 1 year, must now be prepaid prior to travel. The Argentine Embassy in Washington issued a notice that links to the payment website.
Delta issued a press release on Dec 28, the day of implementation for Ezeiza Internaitonal Airport (EZE), that passengers without proof of payment of the reciprocity fee will be denied boarding on flights to Argentina. Aeroparque (AEP) was implemented on October 31.
This only applies to flights to either of Buenos Aires’ airports, Matador has an article on details and workarounds, such as flying to other Argentine cities on regional flights as point of first entry.