Srinagar, Aug. 26 -- A QR code at a roadside stall says something profound about India's economic transformation, so does a fruit grower receiving payment directly from a buyer or an artisan collecting an advance from a customer hundreds of miles away.

UPI has made such transactions routine, while giving India a chance to build something bigger: a financial system where access to opportunity begins with something as simple as receiving a payment.

The Unified Payments Interface, launched by the National Payments Corporation of India on April 11, 2016, under Reserve Bank of India oversight, began with a straightforward idea: moving money should be as easy as sending a message.

It brought banks and payment applications onto one interopera...