It seems almost too good to be true: a mobile app that tracks how many steps you take each day and gives you cash rewards depending on how far you walk.

Now, Chinese authorities say blockchain-based fitness app Qubu might indeed be a scam. Public security officials in central China’s Hunan province are investigating alleged illegal fundraising and financial fraud at the company behind the program amid claims that it operates a Ponzi-like business model.

Qubu works by charging new users 1 yuan ($0.14) to sign up and rewarding those who walk more than 3,000 steps in one day with “candy coins” the company says can be exchanged for real cash through virtual-coin trading platform Global Health Blockchain Club. The app has gained more than 20 million users since its establishment in June last year, according to the developer’s website.

Qubu has been removed from both Apple’s and Android’s app stores but can still be downloaded via invitation codes from other users.

Read the full story on Caixin Global later today.

Contact reporter Isabelle Li (liyi@caixin.com)

Related: Chinese Authorities Warn Against Illegal Crypto Fundraising