PhonePe/Google Pay ↔ Bank UPI API Integration : Mock System Design Interview | MAANG Interview Prep

In this video, I walk through a mock system design interview question:

"Design an integration where PhonePe connects with banks via UPI APIs to support money transfers, balance checks, and mandates."

🎯 This system handles:

Real-time money transfers using secure bank APIs

High-concurrency requests with rate-limiting and retries

Data consistency using the Saga Pattern

Asynchronous processing via Message Queues (Kafka, SQS, etc.)

Webhook handling and reconciliation with banks

Data abstraction and idempotency handling

💬 We also cover:

Availability vs consistency trade-offs

Race condition scenarios and how to avoid them

When to use HMAC over OAuth/mTLS

Real-world system architecture design principles

🧠 Perfect for backend engineers, system designers, and interview prep for companies like PhonePe, Razorpay, Google, Amazon, or other fintech and product companies.

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#SystemDesign #PhonePe #UPI #BackendEngineering #MockInterview #Fintech #Kafka #SagaPattern #Idempotency #TechInterviews

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