Hello,
I book and pay in advance on-line either my bus ticket with Busbud, or directly with Aerolineas Argentinas from Buenos Aires to Posadas.
This is a normal Visa purchase, on the computer, with my mobile bank app running, where I usually have to 'confirm transaction'
How far ahead are you trying to book??
Make sure you really have the website:
https://www.aerolineas.com.ar/
as it is way down the Google page..
Hope this helps...
Cordialement,