I’m not an economist or even a very well versed person in the matter, but it is my understanding that Argentina is always almost out of dollars in its reserves and the local currency has been devaluated steadily since 2001. People figured out rather quickly that holding dollars is the only way to save money, but if let free, the demand would make the exchange rate skyrocket. So the Government (who put us there in the first place) has put limits on how much people can acquire per month.
This of course has implications for the whole economy I’m not equipped to answer or understand, but by “faking ” a lower official rate, most legal business happens at the official rate, while the street market dictates what the real value should be close to.
If you do business internationally and it’s bank to bank and all legal, you exchange at the official rate.
If it’s cash business then you exchange at the blue rate. Or if it’s in Pesos but it’s an imported good, calculate pesos value based on blue value.