Why is Giannis in Miami?! What happened with the Celtics?

Why is Giannis in Miami?! What happened with the Celtics?
Why did the deal fall through? Was it about a 3rd year? Or was it due to Hugo Gonzalez and/or Baylor Scheierman?
Curtis: "If that is true, that is a fire able offense" Let's hear from Shams Charania