Annabelle Huang recently won a government lottery to try China’s latest economics experiment: a national digital currency. After joining the lottery through the social media app WeChat, Huang, 28, a business strategist in Shenzhen, received a digital envelope with 200 electronic Chinese yuan, or eCNY, worth around $30.To spend it, she went to a convenience store near her office and picked out some nuts and yogurt. Then she pulled up a QR code for the digital currency from inside her bank app, which the store scanned for payment.