Startup · Noida
Paytm interviews test payments domain knowledge, backend systems, and data engineering for their fintech ecosystem.
Process: Online Assessment → Technical × 2 → HR
What is Paytm's product portfolio and which engineering domains are most relevant for interviews?
Tip: Paytm (One 97 Communications): payments (wallet, UPI, QR), Paytm Bank, insurance, lending, ticketing, and gaming. Engineering domains: payment systems, wallet management, QR code generation + scanning, notification infrastructure, fraud detection, and data analytics for merchant insights.
Design Paytm's QR code payment acceptance system for small merchants.
Tip: QR encodes: merchant VPA (Virtual Payment Address). Flow: customer scans QR → opens UPI app → enters UPI PIN → initiates push payment to merchant VPA → NPCI routes → merchant gets credit + notification. Static QR: fixed amount. Dynamic QR: encoded with amount + order_id for tracking. Verification: webhook from UPI to Paytm backend.
How does a digital wallet work? Describe the debit and credit flow.
Tip: Wallet: stored-value account. Credit flow: add money → bank transfer (NEFT/UPI) → credit wallet ledger row. Debit flow: payment initiated → check balance (SELECT FOR UPDATE) → debit wallet row → credit merchant. Idempotency: use payment_request_id to prevent double debit on retry. Paytm Wallet must be PPI-compliant (RBI PPI norms).
Write code to find all subsets of a given set (power set).
Tip: Backtracking: at each index, include or exclude the element. O(2^n) time (correct — there are 2^n subsets). Bit manipulation approach: for n elements, iterate 0 to 2^n-1; bit k set → include element k. Paytm coding rounds test classic recursion/backtracking problems.
How would you implement Paytm's KYC (Know Your Customer) verification system?
Tip: RBI-mandated KYC levels: Minimum KYC (₹10K wallet limit, OTP-based) → Full KYC (₹2L limit, Aadhaar eKYC or V-CIP video). Tech flow: Aadhaar OTP → UIDAI API → decrypt response → store encrypted PAN/Aadhaar hash. V-CIP: video call recording, OCR on documents, liveness detection (ML). Data: encrypted, masked in logs.
What is the RBI UPI transaction limit and how does Paytm enforce it technically?
Tip: RBI UPI limits: ₹1L per transaction for P2P, ₹5L for certain merchant categories. Paytm: pre-transaction check against daily/transaction limits stored in a fast KV store (Redis). Also check NPCI response code for bank-imposed limits. Daily limit resets at midnight — use UTC-offset for IST.
Tell me about a time you had to work with legacy code that was critical to business operations.
Tip: Paytm has been operating since 2010 — significant legacy code exists. Show: you documented before touching, added tests before refactoring, made incremental changes (strangler fig pattern) rather than rewrites, and measured metrics before/after. 'It worked for 10 years, respect it before changing it.'
How does Paytm handle the ₹30+ billion in merchant settlements daily?
Tip: Settlement flow: transactions collected throughout day → end-of-day batch → net settlement per merchant → NEFT/IMPS transfer via nodal bank account. T+1 settlement standard. Engineering: batch processing (Spark), reconciliation between Paytm ledger and bank statement, dispute handling (chargeback) queue, RBI-mandated audit logs.
What is two-factor authentication (2FA) and how does Paytm implement it for UPI transactions?
Tip: UPI mandates two-factor auth: Factor 1 = device binding (UPI app registered to this SIM/device). Factor 2 = UPI PIN (6-digit, stored as a hash at the bank, never at Paytm). If SIM is swapped without PIN reset → NPCI can detect via SIM-swap API. Paytm's fraud model flags SIM-swap + large transaction combinations.
Explain eventual consistency in the context of a Paytm wallet transaction.
Tip: User sends ₹100 via Paytm. The payment is immediately marked 'Processing' (optimistic response). Bank debit happens asynchronously. If bank confirms: mark COMPLETE. If bank fails: mark FAILED and reverse the wallet hold. This is a saga pattern — the displayed balance may briefly show the amount on hold.
One 97 Communications (Paytm) interviews follow a 3-round process. Here is what to expect and how to prepare for each stage.
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