System design interview question
"Design a UPI payment flow. A user scans a QR code or enters a payee ID, authorizes with a PIN, and money moves from their bank account to the merchant's — usually in under five seconds. You are the payment app, sitting between the user, the central switch, and multiple banks. 10 billion transactions a month."
orchestrating a multi-party transaction where you control none of the parties. Unlike Stripe (where you own the merchant relationship and settle later), UPI is a real-time, account-to-account rail with a central switch and two banks that each may time out. The distinguishing content is the two-leg debit/credit flow, ambiguous states, and reversal handling.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
Book a free mock interviewAll 132 system design interview questions
System design mock interviews · DSA interview questions · Free mock interview practice · Browse interviewers · Sign in