UPI architecture: VPA, PSP banks and NPCI

UPI turns a bank account into a simple address. The core identifier is the Virtual Payment Address, or VPA, which looks like an email address, for example debarghya@okhdfcbank. The VPA maps to one specific bank account, and the bank that issued the VPA holds the mapping. A payer never needs the payee account number or IFSC, which keeps account details private. When a payment is made, the app sends the VPA and the amount to the payer bank, and the payer bank asks the NPCI switch to route the instruction to the payee bank. NPCI connects every participating bank and settles the net positions between banks through the Reserve Bank of India. Three bank roles can take part in one payment. The Payment Service Provider, or PSP bank, is the bank that provides the UPI service to the app the customer uses, and it authenticates the customer and handles the debit side. The remitter bank holds the payer account, and it is often the same bank as the PSP bank but does not have to be. The beneficiary bank holds the receiver account and credits it. NPCI sits in the middle, switching the messages and managing settlement. An analyst who confuses the PSP bank with the remitter bank will misassign responsibility when a payment fails. A pay request moves through six clear steps. Step one, the payer enters the VPA or scans a QR code, types the amount, and confirms with the UPI PIN. Step two, the app sends a pay request to the PSP bank, which forwards it to the NPCI switch. Step three, NPCI validates the VPA, finds the beneficiary bank, and routes a debit instruction to the remitter bank. Step four, the remitter bank checks the balance and the PIN, debits the payer, and confirms back. Step five, NPCI routes a credit instruction to the beneficiary bank, which credits the payee and confirms. Step six, NPCI sends the final success response to the app. The status at each step is explicit, initiated, debited, credited, or confirmed, and the payment is only complete when the final confirmation arrives. A collect request follows the same path in reverse: a merchant asks the payer for money, the payer approves it with the UPI PIN, and the same debit, credit, and confirmation steps run. A timeout does not mean the payment failed. A timeout happens when one bank or the switch does not respond within the allowed time, so the app cannot tell the customer whether the money moved. The transaction status is pending, not failed, and the money may already have been debited. The correct action is never to send the payment again straight away. The app must first call the check transaction status service, which asks NPCI and the banks for the final status of the original transaction. If the check confirms the credit happened, the app shows success. If the check confirms the debit happened but the credit did not, the remitter bank must reverse the debit. Blind retries are the most common cause of duplicate debits in UPI, so the status check before any retry is a hard rule. Failed transactions and duplicate debits have a fixed remedy. A failed transaction is one where the debit never happened, for example insufficient funds, an invalid VPA, a wrong UPI PIN, or a beneficiary account that cannot accept credits. In that case nothing moves and the customer can correct the detail and try again. A duplicate debit happens when a retry creates a second debit for the same purchase, detected by matching the original transaction reference and amount, and the bank must reverse it. Where a debit happened but the credit did not, the rules require an automatic debit reversal, so the payer gets the money back. Reconciliation must be built around the transaction reference, the only reliable way to match a debit, a credit, a reversal, and a complaint. The scheme rules set the limits an analyst must check. UPI works around the clock, every day of the year, and a normal payment is credited in seconds. The general per transaction limit is one lakh rupees, with higher limits for specific categories such as tax payments, up to five lakh rupees for specified categories since December 2024 (NPCI), and banks may set lower daily limits of their own. Person to person payments are free for the customer, and the UPI PIN authenticates every debit, so a wrong PIN blocks the payment and repeated wrong attempts can lock the facility. Requirements must record the limit, the timeout and reversal behaviour, and the status check flow, because a screen that says failed when the real status is pending will drive the customer to retry and create a duplicate debit.