National Unified USSD Platform
The National Unified USSD Platform (NUUP), also known as the *99# service, is a platform that provides access to the Unified Payment Interface (UPI) service over the USSD protocol. Initiated by the Government of India and developed by the National Payments Corporation of India (NPCI), it facilitates access to banking services from mobile phones.
Source: Wikipedia — National Unified USSD Platform (CC BY-SA 4.0)