In case you are not aware, UPI is basically a rebranded IMPS with Venmo style of address. Until UPI actually works internationally it is still a domestic payment system.
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.