You’re talking about the study where they introduced currency into a contaiment with capuchins.

For some reason, a lot of people must have heard the story as involving bonobos, but anyway:

https://www.zmescience.com/research/how-scientists-tught-monkeys-the-concept-of-money-not-long-after-the-first-prostitute-monkey-appeared/

They gave them little silver disks, just randomly, for a while.

Eventually the monkeys figured out the ‘money’ could be exchanged for grapes, from the researchers.

They kept giving the monkeys ‘money’ randomly, and for doing various tasks.

Then they gave them different kinds of fruit for different prices.

Then they introduced them to gambling, random amount of fruit for a certain price.

Then a monkey stole another monkey’s ‘money’, which caused basically a a free for all monkey riot that involved almost all the monkeys.

… And then shortly after that, the monkeys invented monetarily compensated prostitution, with a male paying a female for sex, which the female immediately afterward purchased a grape with.