Cash payment

Fake news is front and center with the $150 billion dollar transfer to Iran. The story makes it seem like this was money for some favor when in fact the United States merely released funds that had been tied up since the 1979 Iranian revolution. When released Iran had to give over much of this money to debtors. The real story was the $1.8 billion cash in the form of Swiss franks and Euros. Supposedly this was payment for an earlier arms deal but the big question is, why cash? When such deals are in cash it always raises questions and these have never been asked or answered.