TOKYO/HO CHI MINH CITY -- For Vietnamese fintech startup MoMo, the key to winning the battle against Grab, Sea and other rivals for the country's 100 million consumers may be a simple cup of coffee.

Vietnam has witnessed an explosion of digital wallets, such as MoMo, Grab's Moca, ZaloPay and VNPAY, used at businesses like this convenience store in Ho Chi Minh City. (Source photos by Lien Hoang and Ken Kobayashi)
E-wallet app MoMo looks to maintain its lead against deep-pocketed rivals