Abey Lin, a 19-year-old Californian studying at Beijing Film Academy, uses his smartphone to order a local restaurant’s roast duck dish for 20 yuan ($2.99), about 80 percent less than it costs at the register, via delivery app Meituan. Lin, an aspiring director, arrived in Beijing mentally prepared for the hardships of the capital—the blackened air, the bitter winters, the government bans on Instagram and Snapchat.