Another part of this cash transfer was that US dollars were exchanged for Euros. I understand it is illegal to actually transfer US dollars in CASH to Iran.
Also, all the money was not flown to Iran. Some was flown to other banking destinations.
Prior to the 1979 Islamic revolution the Shah’s government had made a payment to the US for aircraft. The aircraft was never delivered. The funds for the aircraft had been held in bank accounts for almost 40 years. It had gained a substantial amount of interest in that time.
What happened, again it’s not discussed much, but $400 million ended up being found in Europe (Swiss Franc, Euro, dollars, etc), and put on a pallet...flown into Tehran. Call it a downpayment, or whatever. The rest flowed later (I think it was four to eight weeks after the first shipment).
Why the cash discussion never came up...has never been explained by bankers or US authorities. Privately, Iranians will suggest that the currency exchange occurred, with tons of Iranian Rials being handed over by the VIP government guys, with a good rate, and the private funds then shipped out of the country.