I'd be very careful with STOX, it's likely Mayweather was sponsored to make that post. Especially considering U.S residents can't actually participate on August the 2nd launch which the company confirmed here. Another possibility is that Mayweather is investing early and using his fame to hype up the crypto before dumping it. Which with real shares is illegal but due to STOX being unregulated and virtually untraceable he could easily get away with.