When India was hit both by the failure of a big bank and a nationwide lockdown in March,
bankers, fearing runs from rattled depositors, rushed to stuff cash machines with notes.
In fact the demand for cash was relatively subdued. Activity hummed along the Unified Payment Interface (UPI),
an electronic-payments network that is on its way to becoming the country's financial lifeline.
Both the identity and the payment layers are controlled by the government, but open to others. As a result, using the system is cheap.
Outside India payments tend to be handled mainly by private firms such as Visa, Mastercard, American Express or, in China, Ant Financial and Tencent.
These own the pipes through which funds flow, and can charge heavily for their use.
Their close relationships with users create high barriers to entry, putting new entrants at a disadvantage. By contrast, UPI is forbidden to charge merchants fees.
India's set-up enables competition. The heavily regulated banking system still holds all the funds.
However, layered on top are a number of lightly regulated private companies, with which customers interact directly.
These apps initiate transactions and have access to account information but do not control money or networks.
Paytm, a home-grown firm, and PhonePe, owned by Walmart, are big players. So too is Google, perhaps explaining its enthusiasm for the system.
But the costs of switching are negligible, requiring just a tap on a phone.
UPI will next step into the realm of lending. Seven "account aggregator" are preparing to launch (although covid-19 has delayed their roll-out).
Once granted a customer's permission, these will compile a history of funds received and paid, which can be shared with lenders.
The benefits of such a system are clear. It would break the links between credit and collateral or personal relationships,
and allow even small lenders to get loans based on their transaction histories and their income.
When combined with cheap transfer costs, the cost of lending to even the tiniest business could fall. These now pay as much as 4% for a one-day loan.
But this is also where the drawbacks of UPI could become most apparent. Only a handful of transactions fail, but glitches have been known to occur.
Aadhaar numbers have leaked before. Security matters more when access to credit is at stake.
Another concern is the extent of the government's control over parts of the infrastructure. In related areas it has not been above misusing its clout.
In 2019, for instance, it shut down the internet in the troubled territory of Kashmir.
Clever as India's digital financial system is, such risks could mean that, for some, cash retains the edge.