Design a virtual card provisioning and transaction system
Last updated: August 6, 2025
Quick Overview
Design the system behind Affirm Card, which provisions virtual debit cards that let consumers split any purchase into installments. Cover card issuance, real-time transaction authorization, and installment plan creation.
Affirm
August 6, 20259
7
2,060 solved
Design the system behind Affirm Card, which provisions virtual debit cards that let consumers split any purchase into installments. Cover card issuance, real-time transaction authorization, and installment plan creation.
The Affirm Card is a strategic product that extends BNPL beyond e-commerce to in-store purchases. This question tests your ability to design systems that interact with card network protocols (Visa/Mastercard) while maintaining Affirm's installment logic.
What the Interviewer Expects
- Design card provisioning with tokenization and secure storage
- Explain the real-time authorization flow when a consumer taps to pay
- Handle the bridge between card network authorization and BNPL plan creation
- Discuss PCI DSS compliance and data security requirements
- Design for sub-100ms authorization response times
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle an authorization request when the credit decisioning service is temporarily unavailable?
- How do you handle authorization reversals and partial captures?
- What happens when a consumer exceeds their spending limit mid-transaction?
- How would you support adding the Affirm Card to Apple Pay and Google Pay?
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Practice System Design ProblemsSample Answer
Requirements
Functional Requirements
- Virtual Card Issuance: Users can apply for a virtual card through the Affirm app, which generates an ISO 8583 compliant virtual card.
- **Real-time Transaction Auth...
Capacity Estimation
Assuming Affirm serves 10 million users, with an average of 1 transaction per user per week:
- Total Transactions per Week: 10 million transactions
- Transactions per Second (TPS): 10 million ...
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