New Delhi, Aug. 17 -- With a total value of Rs.314 trillion, the unified payments interface (UPI) is now the world's largest digital payments system. In roughly a decade since its launch, monthly UPI transaction value has reached nearly 70% of the cash in circulation in India. Its rapid success has prompted the National Payments Corporation of India (NPCI), which administers the system, to seek expansion into more countries beyond the 10 where it currently operates.

Detailed data released last month by PhonePe, which accounts for about half of UPI transactions, suggests that the payment technology is also gaining ground beyond India's biggest cities. To be sure, the PhonePe data may not be nationally representative of the entire UPI mark...