How does UPI work without internet?

UPI works offline using the USSD service by dialing the code *99# from your registered mobile number. This opens an interactive menu that allows you to select options like 'Send Money' or 'Check Balance'. You enter the recipient's details (mobile number or UPI ID), the amount (up to ₹5,000), and authorize the transaction using your UPI PIN. This service is accessible on any mobile phone, even basic feature phones, without needing an internet connection.