Technically based off the same network as ATMs by IDRBT, https://en.m.wikipedia.org/wiki/Institute_for_Development_an...

Unified Payments Interface is built on top of IMPS, with the key architectural work done by the Mobile Payments Forum of India, IIT Madras and IDRBT

It is managed by the National Payments Corporation of India (NPCI) and is built upon the existing National Financial Switch network.