You can switch to Amex, but here in Argentina like half of the postnets don't recognize it.
Also there are a few QR networks, some made by the banks like "Modo" and other no-a-bank ones like "MercadoPago" and a few minor ones. Even the guy/gal that sells hot bread on the street accept most of them.
Amex is only available on Steam in the US. I have a basic free Amex card as a backup, but I wouldn't be able to use it for my Steam purchases. Presumably because the processing fees are just that much higher.
Somehow I'm able to use a JCB card though. As far as I'm aware, JCB cards aren't even available here.
> You can switch to Amex, but here in Argentina like half of the postnets don't recognize it.
To this point, it was even a punchline in The Hitchhiker’s Guide To The Galaxy.