New Delhi, June 11 -- As India's digital payments ecosystem marks a decade of UPI, an old debate is making a comeback.

The fintech industry is once again discussing the possibility of reintroducing a Merchant Discount Rate (MDR) for certain categories of UPI transactions. For years, the issue was largely settled. The success of UPI was built on the principle of keeping digital payments free for consumers and merchants, helping create one of the world's most successful examples of digital public infrastructure.

Today, however, the conversation is returning, not because anyone disputes the success of UPI, but because questions are being raised about how that success should be sustained over the next decade.

Few would argue with the fact ...