FinTech Engineering Interview - Comprehensive Question Bank

Question Classification

Questions are classified across two dimensions:

1. Topic Area - The domain or subject matter
2. Question Type - The format or approach to the question

Topic Areas

• 💳 Payment Processing
• 💱 Transaction Systems
• 🔒 Security & Compliance
• 🚨 Fraud & Risk
• 📊 Data & Analytics
• 🌐 API Design
• 👤 User Experience
• 🔄 System Integration
• ⚙️ Architecture & Scalability
• 📱 Mobile & Frontend

Question Types

• 🏗️ System Design - Design a complete system or architecture
• 🧩 Component Design - Design a specific component or service
• 🔍 Problem Solving - Solve a specific technical problem
• 💻 Coding - Implement a specific algorithm or function
• 🧪 Testing & Quality - Address testing or quality assurance
• 🛡️ Security Implementation - Implement specific security measures
• 📈 Performance Optimization - Optimize for performance
• 🧠 Conceptual - Explain concepts or trade-offs

Question Bank

💳 Payment Processing

🏗️ System Design

1. Design a payment gateway that can handle 10,000 transactions per second while maintaining PCI compliance.
2. Design a system for handling multi-currency payments with real-time exchange rates.
3. Design a subscription billing system with support for various billing cycles and payment methods.
4. Design a payment processing system that can integrate with multiple payment processors with failover capability.
5. Design a split payment system for a marketplace platform.

🧩 Component Design

6. Design a tokenization service for credit card information.
7. Design a retry mechanism for failed payment transactions.
8. Design a service for handling payment webhooks from multiple providers.
9. Design a reconciliation system for matching payment processor reports with internal records.
10. Design a refund processing system with support for partial refunds.

🔍 Problem Solving

11. How would you handle idempotency in payment processing?
12. How would you implement proper error handling for payment failures?
13. How would you handle settlement across different time zones and banking systems?
14. How would you manage payment processor API rate limits?
15. How would you implement dynamic routing between payment processors based on cost and success rates?

💻 Coding

16. Implement a Luhn algorithm validator for credit card numbers.
17. Write a function to calculate installment payment amounts for different payment plans.
18. Implement a basic tokenization function for credit card numbers that preserves the last four digits.
19. Write a function to validate international bank account numbers (IBAN).
20. Implement a function to calculate payment processing fees based on complex rule sets.

💱 Transaction Systems

🏗️ System Design

21. Design a real-time transaction processing system that ensures consistency across distributed databases.
22. Design a double-entry accounting system for financial transactions.
23. Design a ledger system that maintains an immutable audit trail of all transactions.
24. Design a system for processing ACH transfers with appropriate retry mechanisms.
25. Design a real-time balance system that prevents overdrafts.

🧩 Component Design

26. Design a transaction journaling system that enables recovery after failures.
27. Design a service that manages transaction state through a complex workflow.
28. Design a component for handling currency conversion in international transactions.
29. Design a system for tracking transaction status across multiple services.
30. Design a batching system for high-volume transaction processing.

🔍 Problem Solving

31. How would you ensure atomicity in distributed financial transactions?
32. How would you handle eventual consistency in a financial reporting system?
33. How would you implement transaction isolation in a microservices architecture?
34. How would you resolve a situation where transactions are out of sync across systems?
35. How would you implement compensating transactions for rollbacks in distributed systems?

💻 Coding

36. Implement a simplified version of a two-phase commit protocol.
37. Write a function to detect and prevent double-spending in a transaction system.
38. Implement a basic ledger system with debit and credit operations that ensures balance.
39. Write a function to calculate compound interest with various compounding frequencies.
40. Implement a transaction rate limiter with a sliding window algorithm.

🔒 Security & Compliance

🏗️ System Design

41. Design a secure authentication system for a banking application.
42. Design a system for storing and processing credit card information compliant with PCI DSS.
43. Design a key management system for a financial application.
44. Design a secure audit logging system for financial transactions that satisfies regulatory requirements.
45. Design a system that implements appropriate access controls for different roles in a financial application.

🧩 Component Design

46. Design a secure session management system for a banking application.
47. Design a service for securely sharing sensitive financial data between systems.
48. Design a secure password reset flow for a financial application.
49. Design a component for handling secure file uploads containing financial information.
50. Design a secure API key management system.

🔍 Problem Solving

51. How would you implement field-level encryption for sensitive data?
52. How would you handle secure credential storage?
53. How would you implement GDPR's "right to be forgotten" in a financial system while maintaining regulatory compliance?
54. How would you detect and prevent session hijacking attacks?
55. How would you implement proper certificate management for a financial API?

🛡️ Security Implementation

56. Implement a secure data masking solution for financial reports.
57. How would you implement Content Security Policy for a banking web application?
58. Design and implement a solution for preventing CSRF attacks on financial transactions.
59. Implement a secure approach for storing API keys in a microservices environment.
60. How would you implement proper input validation for international financial data?

🚨 Fraud & Risk

🏗️ System Design

61. Design a real-time fraud detection system for payment transactions.
62. Design a risk scoring system for loan applications.
63. Design an anti-money laundering (AML) detection system.
64. Design a system for detecting and preventing account takeover attacks.
65. Design a chargeback and dispute management system.

🧩 Component Design

66. Design a feature store for real-time fraud detection.
67. Design a rules engine for transaction risk assessment.
68. Design a service for behavioral biometrics analysis.
69. Design a system for device fingerprinting to detect suspicious logins.
70. Design a component for velocity checking across multiple dimensions.

🔍 Problem Solving

71. How would you balance false positives and false negatives in a fraud detection system?
72. How would you detect coordinated fraud across multiple accounts?
73. How would you handle model drift in a production fraud detection system?
74. How would you implement features that detect unusual patterns in transaction behavior?
75. How would you create an explainable fraud detection system for regulatory requirements?

💻 Coding

76. Implement an algorithm to detect anomalies in transaction patterns.
77. Write a function to calculate a basic risk score based on multiple factors.
78. Implement a simplified version of a rules engine for transaction validation.
79. Write code to detect potential velocity abuse across multiple accounts.
80. Implement a function to identify potentially linked accounts based on common attributes.

📊 Data & Analytics

🏗️ System Design

81. Design a data pipeline for processing financial transactions for analytics.
82. Design a real-time dashboard system for monitoring financial metrics.
83. Design a data warehouse architecture for financial reporting.
84. Design a recommendation system for financial products.
85. Design a customer segmentation system for a bank.

🧩 Component Design

86. Design a feature engineering pipeline for credit risk models.
87. Design a system for A/B testing financial product features.
88. Design a data lineage tracking system for regulatory reporting.
89. Design a component for generating financial regulatory reports.
90. Design a system for customer lifetime value prediction.

🔍 Problem Solving

91. How would you handle slowly changing dimensions in financial data warehousing?
92. How would you ensure data quality in financial pipelines?
93. How would you implement real-time aggregations for financial dashboards?
94. How would you handle bias in financial machine learning models?
95. How would you approach feature selection for a credit risk model?

💻 Coding

96. Implement a function to calculate financial KPIs from transaction data.
97. Write code to perform cohort analysis on customer financial data.
98. Implement a basic anomaly detection algorithm for financial time series.
99. Write a function to create a customer segmentation model using financial behavior.
100. Implement a function to generate a financial forecast using historical data.

🌐 API Design

🏗️ System Design

101. Design an API gateway for a financial services platform.
102. Design a versioning strategy for financial APIs.
103. Design an API system for open banking compliance.
104. Design a webhook delivery system for financial events.
105. Design a comprehensive API documentation system for financial services.

🧩 Component Design

106. Design an API rate limiting service for financial endpoints.
107. Design a service for API key rotation and management.
108. Design a contract testing system for financial APIs.
109. Design an API monitoring and alerting system.
110. Design a service for API request validation and transformation.

🔍 Problem Solving

111. How would you handle backward compatibility in API evolution?
112. How would you implement proper error responses for financial APIs?
113. How would you handle long-running operations in a RESTful API?
114. How would you approach API security for third-party integrations?
115. How would you implement proper pagination for large financial datasets?

💻 Coding

116. Implement a basic API throttling mechanism.
117. Write a function to validate and transform API requests.
118. Implement a middleware for API authentication and authorization.
119. Write a function to generate API documentation from code.
120. Implement a circuit breaker for API calls to external services.

👤 User Experience

🏗️ System Design

121. Design a secure and user-friendly checkout experience.
122. Design a financial dashboard showing transaction history and account status.
123. Design a mobile banking authentication experience that balances security and usability.
124. Design a system for providing personalized financial insights to users.
125. Design an onboarding flow for a financial application with KYC requirements.

🧩 Component Design

126. Design a component for securely collecting credit card information.
127. Design an interactive transaction history visualization.
128. Design a notification system for financial events and alerts.
129. Design a component for guiding users through complex financial decisions.
130. Design a secure document upload system for identity verification.

🔍 Problem Solving

131. How would you optimize loading performance for a financial dashboard?
132. How would you implement form validation for international payment information?
133. How would you handle accessibility requirements for financial interfaces?
134. How would you approach localization for a global financial application?
135. How would you securely store user preferences and settings?

💻 Coding

136. Implement a mask/unmask toggle for sensitive financial information.
137. Write a function to format currency values according to different locales.
138. Implement input validation for a credit card form with real-time feedback.
139. Write a component that visualizes spending patterns by category.
140. Implement secure local storage for user session handling.

🔄 System Integration

🏗️ System Design

141. Design a system for integrating with multiple banking APIs.
142. Design an architecture for integrating with legacy financial systems.
143. Design a system for real-time market data integration.
144. Design a system for integrating with multiple credit bureau APIs.
145. Design a system for integrating with regulatory reporting systems.

🧩 Component Design

146. Design an adapter layer for different payment processor APIs.
147. Design a service for normalizing data from different financial sources.
148. Design a system for managing API credentials for multiple external services.
149. Design a retry and circuit breaker system for external API calls.
150. Design a system for handling webhook events from multiple sources.

🔍 Problem Solving

151. How would you handle inconsistent data formats across different financial APIs?
152. How would you manage dependencies on third-party financial services?
153. How would you handle version changes in integrated financial APIs?
154. How would you implement fallback mechanisms for critical integrations?
155. How would you validate data consistency across integrated systems?

💻 Coding

156. Implement an adapter pattern for multiple payment processor APIs.
157. Write a function to transform data between different API formats.
158. Implement a webhook signature verification system.
159. Write a service discovery function for dynamically finding integration endpoints.
160. Implement a function for synchronizing data between systems with conflict resolution.

⚙️ Architecture & Scalability

🏗️ System Design

161. Design a multi-region architecture for a global payment system.
162. Design a microservices architecture for a banking platform.
163. Design a system architecture that can handle seasonal traffic spikes for a tax filing service.
164. Design a high-availability architecture for a trading platform.
165. Design an event-driven architecture for a financial services platform.

🧩 Component Design

166. Design a caching strategy for financial data with consistency requirements.
167. Design a database sharding approach for financial transaction data.
168. Design a service discovery system for a microservices-based financial platform.
169. Design a circuit breaker implementation for a financial services platform.
170. Design a message queue architecture for asynchronous financial processing.

🔍 Problem Solving

171. How would you handle database failover in a financial transaction system?
172. How would you implement zero-downtime deployments for a payment processing system?
173. How would you approach capacity planning for a financial system with seasonal usage patterns?
174. How would you implement proper observability in a distributed financial system?
175. How would you design for disaster recovery in a multi-region financial platform?

📈 Performance Optimization

176. How would you optimize database performance for high-volume financial transactions?
177. How would you reduce API latency for critical financial operations?
178. How would you implement efficient caching for frequently accessed financial data?
179. How would you optimize a slow-performing financial reporting query?
180. How would you approach performance testing for a high-load financial system?

📱 Mobile & Frontend

🏗️ System Design

181. Design a mobile banking app architecture.
182. Design a system for offline functionality in a financial mobile app.
183. Design a secure local storage strategy for financial data in a mobile app.
184. Design a real-time trading interface that updates market data efficiently.
185. Design a responsive financial dashboard that works across devices.

🧩 Component Design

186. Design a secure biometric authentication component for a financial app.
187. Design a component for scanning and processing payment cards.
188. Design an efficient data synchronization mechanism for a financial mobile app.
189. Design a component for secure document capture and upload.
190. Design a notification system for financial alerts in a mobile app.

🔍 Problem Solving

191. How would you handle secure authentication token storage in a mobile app?
192. How would you implement secure communication between a mobile app and financial APIs?
193. How would you optimize image processing for check deposits in a banking app?
194. How would you handle poor network conditions in a financial mobile app?
195. How would you implement proper error handling and recovery in a financial UI?

💻 Coding

196. Implement a secure local storage mechanism for sensitive financial data.
197. Write a function to efficiently update UI components with real-time financial data.
198. Implement input masking and validation for financial form fields.
199. Write a component for visualizing financial time series data.
200. Implement a state management approach for a complex financial form with multiple steps.

Question Hint Sheet

💳 Payment Processing

1. Payment gateway (10k TPS): Consider separate paths for authorization vs. capture, tokenization for PCI compliance, horizontal scaling with stateless services, and idempotency implementation. Edge cases: Processor outages, partial system failures, traffic spikes during sales events.

2. Multi-currency payments: Consider exchange rate source, rate caching strategy, conversion timing (display vs. processing), and handling currency precision. Edge cases: Volatile exchange rates, unsupported currency pairs.

3. Subscription billing: Consider billing cycle management, retry strategies for failed payments, proration for plan changes, and dunning management. Edge cases: Mid-cycle plan changes, payment method expirations.

4. Multi-processor integration: Consider abstraction layer, consistent response mapping, routing logic, and failover strategy. Edge cases: Different feature support across processors, inconsistent response formats.

5. Split payment system: Consider transaction atomicity, failure handling when some splits succeed while others fail, and reconciliation requirements. Edge cases: Refunds on split payments, uneven splits with rounding issues.

6. Tokenization service: Consider token format, storage security, scope limitation, and PCI compliance requirements. Edge cases: Token collisions, migration between token systems.

7. Payment retry mechanism: Consider exponential backoff, retry limits, idempotency, and state tracking. Edge cases: Distinguishing permanent vs. temporary failures.

8. Webhook handling: Consider signature verification, idempotency, delivery guarantees, and retry mechanisms. Edge cases: Out-of-order webhook delivery, duplicate webhooks.

9. Reconciliation system: Consider matching algorithms for inexact matches, exception handling, and manual review workflows. Edge cases: Fee variations, currency conversion differences, timing issues.

10. Refund processing: Consider partial refunds, multiple refunds up to original amount, and status tracking. Edge cases: Refunds after long periods, refunds to expired payment methods.

11. Idempotency in payments: Consider idempotency key generation, storage/TTL, and verification strategies. Edge cases: Client retry with different payload, very delayed retries.

12. Payment error handling: Consider categorizing errors (permanent vs. temporary), user-facing vs. internal errors, and recovery paths. Edge cases: Indeterminate states, third-party timeouts.

13. Cross-timezone settlement: Consider banking hours in different regions, cut-off times, and date rollover handling. Edge cases: Holiday calendars across regions, DST transitions.

14. API rate limits: Consider rate limit pools, prioritization strategies, and graceful degradation. Edge cases: Burst traffic patterns, critical vs. non-critical operations.

15. Dynamic processor routing: Consider success rate monitoring, cost optimization, and smart routing algorithms. Edge cases: Conflicting optimization criteria, processor-specific features.

16-20. Coding questions: Focus on input validation, edge cases handling (like zero values, negative amounts), internationalization support, and proper decimal handling for currency.

💱 Transaction Systems

21. Real-time transaction system: Consider ACID properties, distributed transaction patterns (saga vs. 2PC), and consistency models. Edge cases: Network partitions, partial failures.

22. Double-entry accounting: Consider balanced transactions across accounts, immutable transaction records, and reconciliation processes. Edge cases: Rounding issues, multi-currency balancing.

23. Immutable audit trail: Consider append-only design, cryptographic verification, and secure storage. Edge cases: High-volume performance, compliance with "right to be forgotten".

24. ACH processing: Consider state machine design, retry strategies specific to ACH failure modes, and status tracking. Edge cases: Return codes handling, holiday processing.

25. Real-time balance system: Consider optimistic vs. pessimistic locking, preauthorization holds, and consistency guarantees. Edge cases: Concurrent transactions, auth+capture flows.

26. Transaction journaling: Consider write-ahead logging, crash recovery procedures, and performance optimization. Edge cases: Journal corruption, out-of-order recovery.

27. Transaction state management: Consider state machine design, idempotent transitions, and timeout handling. Edge cases: Stuck transactions, manual intervention processes.

28. Currency conversion: Consider rate sources, conversion timing, precision handling, and rate caching. Edge cases: Rate fluctuations, triangular arbitrage.

29. Transaction status tracking: Consider event-driven updates, eventual consistency handling, and timeout/expiration policies. Edge cases: Lost events, system restart recovery.

30. Transaction batching: Consider atomicity guarantees, optimal batch sizes, and failure handling. Edge cases: Partial batch failures, priority items in batches.

31-40. Problem solving & coding: Focus on consistency guarantees, race condition prevention, proper transaction isolation levels, and compensating transaction patterns.

🔒 Security & Compliance

41. Secure authentication: Consider MFA options, risk-based authentication, and session management. Edge cases: Account recovery, device migration.

42. PCI-compliant storage: Consider tokenization, scope reduction, and network segmentation. Edge cases: Historical data migration, vendor compliance.

43. Key management system: Consider key hierarchy, rotation policies, and secure storage. Edge cases: Key compromise procedures, disaster recovery.

44. Audit logging: Consider tamper resistance, retention policies, and privileged access monitoring. Edge cases: High volume performance, sensitive data filtering.

45. Role-based access: Consider principle of least privilege, dynamic permissions, and separation of duties. Edge cases: Emergency access procedures, nested roles.

46. Session management: Consider token-based approaches, secure storage, and timeout policies. Edge cases: Multiple device login, privileged operation reauthentication.

47. Secure data sharing: Consider end-to-end encryption, access controls, and key distribution. Edge cases: Key rotation, revocation procedures.

48. Password reset flow: Consider out-of-band verification, time-limited tokens, and phishing prevention. Edge cases: Account takeover attempts, lost access to verification channels.

49. Secure file uploads: Consider content validation, malware scanning, and secure storage. Edge cases: Large file handling, malicious document detection.

50. API key management: Consider distribution, rotation, and principle of least privilege. Edge cases: Compromised key handling, emergency rotation.

51-60. Security implementation: Focus on defense in depth, secure default settings, and compliance with financial regulations like PCI DSS, SOC2, and GDPR.

🚨 Fraud & Risk

61. Fraud detection system: Consider real-time scoring, rules engines with ML models, and feedback loops. Edge cases: Model drift, adversarial attacks.

62. Loan risk scoring: Consider multiple data sources, model explainability, and regulatory compliance. Edge cases: Thin-file applicants, newly launched products.

63. AML detection: Consider pattern recognition, behavior profiling, and regulatory reporting. Edge cases: False positive management, investigation workflows.

64. Account takeover prevention: Consider behavior analysis, device fingerprinting, and step-up authentication. Edge cases: Legitimate account transfers, lost device scenarios.

65. Chargeback management: Consider evidence collection, case management, and representment processes. Edge cases: Friendly fraud, time-limited response windows.

66. Feature store: Consider real-time feature computation, historical feature aggregation, and feature freshness. Edge cases: Missing features, cold start problems.

67. Rules engine: Consider performance optimization, rule conflict resolution, and version management. Edge cases: Rule explosion, complex interdependencies.

68. Behavioral biometrics: Consider data collection, privacy implications, and false positive rates. Edge cases: Accessibility considerations, device changes.

69. Device fingerprinting: Consider browser/device limitations and privacy regulations. Edge cases: Legitimate privacy tools usage, shared device detection.

70. Velocity checking: Consider multi-dimensional analysis, time window selection, and baseline determination. Edge cases: False positives during sales/promotions.

71-80. Problem solving & coding: Focus on balancing detection rates with false positives, explainability for regulatory requirements, and real-time performance constraints.

📊 Data & Analytics

81. Financial transaction pipeline: Consider data privacy, schema evolution, and audit requirements. Edge cases: High volume performance, handling sensitive fields.

82. Real-time dashboard: Consider data freshness SLAs, efficient updates, and aggregation strategies. Edge cases: High cardinality dimensions, long-tail distributions.

83. Financial data warehouse: Consider historization strategies, slowly changing dimensions, and compliance requirements. Edge cases: Schema evolution, audit support.

84. Financial product recommendations: Consider personalization factors, compliance constraints, and testing frameworks. Edge cases: Cold start problem, new product launches.

85. Customer segmentation: Consider feature selection, cluster stability, and actionability. Edge cases: Micro-segments, evolving customer behavior.

86. Feature engineering pipeline: Consider domain knowledge incorporation, feature stability, and real-time vs. batch. Edge cases: Missing data handling, outlier treatment.

87. A/B testing system: Consider statistical significance, guardrail metrics, and segment analysis. Edge cases: Low traffic features, network effects.

88. Data lineage tracking: Consider automated capture, versioning, and query capabilities. Edge cases: Complex transformations, external data sources.

89. Regulatory reporting: Consider accuracy validation, reconciliation processes, and submission workflows. Edge cases: Requirement changes, cross-border variations.

90. Customer lifetime value: Consider predictive vs. historical approaches, segmentation factors, and update frequency. Edge cases: Changing product offerings, market disruptions.

91-100. Problem solving & coding: Focus on data quality, efficient processing of large datasets, and statistical validity of analytical approaches.

🌐 API Design

101. API gateway: Consider authentication, rate limiting, and request routing. Edge cases: Circuit breaking, service discovery.

102. API versioning: Consider compatibility policies, deprecation strategies, and client migration support. Edge cases: Long-term support for critical clients, emergency changes.

103. Open banking API: Consider regulatory compliance, consent management, and standardization. Edge cases: Third-party app management, revocation.

104. Webhook delivery: Consider retry policies, delivery guarantees, and monitoring. Edge cases: Endpoint availability issues, out-of-order delivery.

105. API documentation: Consider automated generation, interactive testing, and example workflows. Edge cases: Complex authentication flows, error scenario documentation.

106. Rate limiting: Consider token bucket vs. leaky bucket algorithms, client identification, and response headers. Edge cases: Distributed rate limiting, priority overrides.

107. API key rotation: Consider zero-downtime rotation, deprecation periods, and revocation processes. Edge cases: Emergency revocation, audit requirements.

108. Contract testing: Consider producer vs. consumer driven approaches and test environments. Edge cases: Backward compatibility testing, optional field handling.

109. API monitoring: Consider latency metrics, error rates, and alerting thresholds. Edge cases: Intermittent failures, dependency issues.

110. Request validation: Consider input sanitization, schema validation, and transformation pipelines. Edge cases: Schema evolution, internationalization.

111-120. Problem solving & coding: Focus on backward compatibility, proper error handling, and security considerations for financial API design.

👤 User Experience

121. Checkout experience: Consider form design, error handling, and progress indication. Edge cases: Session expiration, payment method failures.

122. Financial dashboard: Consider data visualization, performance optimization, and information hierarchy. Edge cases: Mobile responsiveness, accessibility.

123. Mobile authentication: Consider biometrics, device binding, and risk-based approaches. Edge cases: New device onboarding, account recovery.

124. Financial insights: Consider relevance algorithms, timing of delivery, and actionability. Edge cases: Data privacy, opt-out capabilities.

125. KYC onboarding: Consider drop-off reduction, clear instructions, and progress saving. Edge cases: Document verification failures, manual review workflows.

126. Credit card collection: Consider PCI compliance, input formatting, and validation. Edge cases: Card type detection, progressive enhancement.

127. Transaction visualization: Consider grouping strategies, search/filter capabilities, and export options. Edge cases: High-volume users, complex transaction types.

128. Financial notifications: Consider delivery channels, urgency levels, and user control. Edge cases: Notification fatigue, critical alert differentiation.

129. Financial decision guidance: Consider explanation clarity, personalization, and bias avoidance. Edge cases: Edge financial situations, regulatory considerations.

130. Document upload: Consider validation feedback, progress indication, and error recovery. Edge cases: Large files, slow connections.

131-140. Problem solving & coding: Focus on usability, performance, accessibility, and security considerations specific to financial interfaces.

🔄 System Integration

141. Banking API integration: Consider normalization layer, credential management, and error handling. Edge cases: API downtime, inconsistent responses.

142. Legacy system integration: Consider data mapping, synchronization strategies, and monitoring. Edge cases: Schema mismatches, performance constraints.

143. Market data integration: Consider real-time processing, data normalization, and failover. Edge cases: Data gaps, high volatility periods.

144. Credit bureau integration: Consider secure credential handling, request optimization, and response normalization. Edge cases: Service outages, scoring discrepancies.

145. Regulatory reporting: Consider data validation, submission workflows, and audit trails. Edge cases: Requirement changes, submission deadlines.

146. Payment processor adapters: Consider common interface design, processor-specific features, and error mapping. Edge cases: Feature parity issues, version variations.

147. Data normalization: Consider schema mapping, transformation rules, and quality validation. Edge cases: Unknown formats, partial data.

148. API credential management: Consider secure storage, rotation policies, and access controls. Edge cases: Credential leakage, emergency rotation.

149. Retry and circuit breaking: Consider failure categorization, backoff strategies, and state persistence. Edge cases: Distinguishing transient vs. permanent failures.

150. Multi-source webhooks: Consider source verification, event normalization, and processing prioritization. Edge cases: Event ordering, duplicate handling.

151-160. Problem solving & coding: Focus on resilience patterns, data consistency, and security considerations for financial integrations.

⚙️ Architecture & Scalability

161. Multi-region architecture: Consider data sovereignty, active-active vs. active-passive, and synchronization. Edge cases: Region failure, cross-region consistency.

162. Microservices for banking: Consider service boundaries, transaction management, and interaction patterns. Edge cases: Distributed transactions, service discovery.

163. Seasonal traffic handling: Consider auto-scaling, capacity planning, and resource optimization. Edge cases: Unexpected traffic patterns, degradation strategies.

164. High-availability trading: Consider failover strategies, data consistency, and latency optimization. Edge cases: Market volatility, partial system failures.

165. Event-driven architecture: Consider event schemas, delivery guarantees, and processing order. Edge cases: Event sourcing, exactly-once processing.

166. Financial data caching: Consider invalidation strategies, consistency requirements, and staleness tolerance. Edge cases: Cache poisoning, thundering herd.

167. Database sharding: Consider sharding keys, cross-shard queries, and rebalancing strategies. Edge cases: Hot shards, shard splits.

168. Service discovery: Consider registration mechanisms, health checking, and failover. Edge cases: Split-brain scenarios, network partitions.

169. Circuit breaker design: Consider failure thresholds, half-open state testing, and fallback strategies. Edge cases: Cascading failures, false positives.

170. Message queue architecture: Consider delivery guarantees, dead letter handling, and scaling. Edge cases: Queue backlog management, priority messages.

171-180. Problem solving & performance: Focus on reliability patterns, disaster recovery, and performance optimization for high-scale financial systems.

📱 Mobile & Frontend

181. Mobile banking architecture: Consider offline capabilities, security model, and feature modularity. Edge cases: App background behavior, deep linking.

182. Offline functionality: Consider data synchronization, conflict resolution, and security constraints. Edge cases: Long offline periods, version conflicts.

183. Secure local storage: Consider encryption, key management, and secure deletion. Edge cases: Device compromise scenarios, app uninstall/reinstall.

184. Real-time trading interface: Consider data streaming, efficient rendering, and state management. Edge cases: High frequency updates, network interruptions.

185. Responsive financial dashboard: Consider data prioritization, progressive loading, and device optimization. Edge cases: Small screens, touch interfaces.

186. Biometric authentication: Consider fallback mechanisms, security levels, and platform integration. Edge cases: Biometric changes, hardware limitations.

187. Payment card scanning: Consider camera access, OCR optimization, and manual fallback. Edge cases: Low light conditions, unusual card designs.

188. Data synchronization: Consider conflict resolution, bandwidth optimization, and progress indication. Edge cases: Partial synchronization, prioritization.

189. Document capture: Consider image quality validation, secure transmission, and storage. Edge cases: Low quality images, large file handling.

190. Mobile notifications: Consider delivery channels, critical vs. non-critical, and user preferences. Edge cases: Notification permissions, delivery timing.

191-200. Problem solving & coding: Focus on security considerations, user experience, and performance optimization for financial mobile applications.