From the FAQ at the bottom of the page.
Skill Gaming: Ready-Go Tournaments and Match Play Challenges fall under Skill Gaming, which certain countries and US states prohibit.
The U.S. states that do not allow skill-based gaming are: Arizona,
Arkansas, Connecticut, Delaware, Florida, Iowa, Illinois, Louisiana,
Maryland, Montana, South Carolina, South Dakota, Tennessee, and Vermont
The countries that do not allow skill-based gaming are: Brazil, Argentina, the People's Republic of China, South Korea, Japan.
Happy hitting