But it's odd, the end results of the "negotiation" are public. So regardless of how the negotiation (or not) happened, the end results (pay package) was in front of them in black and white to decide on.
https://www.sec.gov/Archives/edgar/data/1318605/000119312518...
It was pretty straightforward - if stock price hits X, Elon gets Y. It even says "Elon will own 12% of the company if all stock vests from hitting $650B in valuation".
It even has a nice bar chart showing how much Elon would make if he hit the highest tier - CEO Value Realized ($B) - $55.8