The real David Packouz appears in the movie, singing "Don't Fear The Reaper" in the retirement home where Miles Teller tries to sell sheets.
The real Efraim Diveroli declined to meet with Jonah Hill. Hill said "I'm used to it. If a person is aggressively against me playing them, it's probably a good sign."
At the time that she got the role, Ana de Armas barely spoke any English; she simply learned all her lines phonetically. The makers got wind of this when a line in the script was changed, and she didn't know how to properly pronounce it, or have even a basic conversation. Her management immediately put her through English lessons. Afterwards, she said that she mastered the language in a very short time because her life depended on it.
In this film, Efraim (Jonah Hill) becomes angry at an employee who criticizes the letters in the name AEY for not standing for anything. In real life, the initials do mean something. The company had at first been a shell company started by Efraim's father. The letters in the name are the initials of his children, Aaron, Avigail, Avrohom, Efraim, and Yeshaya.
Jonah Hill gained 44 pounds for the role.