NPCI is state funded and runs at a loss. i.e. your taxes are paying for it.
It's also not the full picture to call them state funded. They're owned by a consortium of banks, both private and public. While the state maintains a level of ownership through their equity in public banks, the company itself is self- sustainable from an operations point of view.
https://bfsi.economictimes.indiatimes.com/news/fintech/upi-t...
The government gives Rs 1,300 crore as subsidy
Unsurprisingly, there is now a 1.1% interchange on some UPI transactions now: https://www.onmanorama.com/news/business/2023/03/31/upi-tran...
Separately, NCPI's revenues are USD ~2B/year: https://www.icra.in/Rationale/ShowRationaleReport/?Id=122149....