Srinagar, Sept. 19 -- By Wahid Gull

India's latest UPI framework creates an unusual economic experiment.

The Finance Ministry says person-to-person payments remain free, as do merchant payments up to Rs.2,000, while a 0.4% Merchant Discount Rate, or MDR, applies to specified merchant transactions above that threshold.

The charge belongs to the merchant-payment system, with the government saying customers themselves will not pay it.

The policy question is familiar: who pays, how much and for what kind of transaction?

The deeper question is harder and more interesting: what price makes a person change the way they spend money?

That question lies at the centre of an economic idea called Marginal Monetary Sacrifice.

The concept asks ho...