Payments / Beginner / 6 min
How a UPI payment works
Your app, NPCI and two banks. Make the shop’s bank slow or down and see pending payments, late credits and auto-reversals.
Start the simulation → Change the load, break a part, watch what happens. Free, no sign-up.
In short
- What it is
- UPI moves money between any two Indian bank accounts in seconds: the payer’s app sends the request to NPCI, which debits one bank and credits the other.
- Why it matters
- Billions of payments a month cross different apps and banks, so every step needs a clear outcome even when a bank times out.
- The trade-off
- A timeout after the debit leaves money in limbo; the system marks it pending and resolves it by status checks and reversals, which can take hours.
- Say it in an interview
- "Every request carries a unique transaction id; on timeout we mark it pending, poll the status API, and rely on NPCI reconciliation to credit or reverse."
Check yourself
In a UPI payment, who connects your bank to the shop’s bank?
Answer: The NPCI switch. Your app (a PSP) talks to NPCI, which routes the debit to your bank and the credit to the payee’s bank.
Your money was debited but the shop’s bank did not answer. What do you see?
Answer: Pending: it either completes or is reversed to you. The debit happened, so the payment cannot simply fail; it stays pending until the credit is confirmed or NPCI reverses it.
Which failure is the "safest"?
Answer: Payer bank down before the debit. If the payer bank is down, nothing is debited and the payment is declined at once. Failures after the debit need reversal.