Did you and the billionaire both sign a written agreement stipulating mandatory investment upon completion of agreed-upon milestones? Do you also have clear do

Did you and the billionaire both sign a written agreement stipulating mandatory investment upon completion of agreed-upon milestones? Do you also have clear documentation showing that you delivered the milestones to the satisfaction of the billionaire? If yes to both, find a local contracts lawyer and give them a call. If no to either, you are unlikely to do more than waste your money/time and should treat it as a shitty learning experience not to trust people in these situations.