>> smartphones are necessary to pay via UPI
No.
[1] UPI money transfer without Internet or smartphone; know how to do it - https://www.businesstoday.in/industry/banks/story/upi-money-...
No.
[1] UPI money transfer without Internet or smartphone; know how to do it - https://www.businesstoday.in/industry/banks/story/upi-money-...
There are areas without reliable mobile coverage... where people who need aadhaar authentication OTPs for their livelihood now, thanks to overzealous implementation of technology, are adversely impacted.
The suggestion is to assume that there are people who cannot use UPI and other shiny new tech, and make accommodations for them to lead their lives, rather than push for all digital and exclude some people.