When I last visited Argentina Uber was using the official exchange rates which were just fantasy numbers. As soon as you match with a driver they’d message you and you’d negotiate the cash price. Then the ride in the app would be cancelled.
Uber didn’t mind because they were still getting the ~$1 or so cancel fee for basically being a messaging app.
If anyone wants to see this in video form watch 90 Day Fiance on TLC. The Ukrainian women seem to be the ultimate masters of it.