Description

This curriculum spans the technical, operational, and regulatory dimensions of payment processing in ways comparable to a multi-workshop architecture review and risk assessment series conducted during a global fintech platform rollout.

Module 1: Payment Gateway Integration Architecture

Select between redirect-based (e.g., hosted payment pages) and direct API integration based on PCI compliance scope and user experience requirements.
Implement idempotency keys in payment initiation requests to prevent duplicate transactions during network retries.
Configure webhook endpoints with TLS 1.2+ and validate payloads using provider-signed secrets to prevent spoofing.
Design fallback routing to secondary gateways during primary provider outages using health checks and circuit breakers.
Map gateway-specific error codes to standardized application-level error types for consistent user messaging.
Isolate sensitive gateway credentials using environment-specific secrets management (e.g., Hashicorp Vault or AWS Secrets Manager).

Module 2: PCI DSS Compliance and Data Handling

Architect card data flows to avoid storage; use tokenization from gateways or a PCI-validated service like Stripe Elements or Braintree.
Implement network segmentation to isolate systems that handle PANs, even if transiently, from general application infrastructure.
Conduct quarterly external vulnerability scans and annual penetration tests when handling card data directly.
Define and enforce strict access controls for logs that may contain truncated card numbers or authorization responses.
Document and maintain an Attestation of Compliance (AOC) when operating in SAQ D environments.
Design logging pipelines to redact sensitive fields (CVV, full PAN) at ingestion using parsing rules or middleware filters.

Module 3: Fraud Detection and Risk Management

Integrate device fingerprinting (e.g., FingerprintJS or MaxMind) to correlate transaction attempts across sessions.
Configure velocity rules to flag or block transactions exceeding thresholds (e.g., 5 attempts from one IP in 10 minutes).
Balance AVS and CVV verification enforcement against conversion rates, especially for international cardholders.
Implement adaptive authentication challenges (e.g., 3D Secure 2) based on risk score thresholds from internal or gateway models.
Establish a process to review and classify chargeback reasons for feedback into fraud rule tuning.
Feed transaction outcomes into a machine learning pipeline to refine risk scoring over time using historical dispute data.

Module 4: Recurring Billing and Subscription Lifecycle

Model subscription states (active, past due, canceled) with explicit transitions and audit trails for compliance.

Implement dunning management workflows with staged email notifications and payment retry schedules.

Synchronize billing periods across prorated plan changes using epoch alignment or anchor billing dates.

Handle tax calculation at subscription creation and renewal using real-time APIs like Avalara or TaxJar.

Design idempotent invoice generation to prevent duplicate billing during system retries or failures.

Support mid-cycle upgrades/downgrades with proration logic that respects billing cycle boundaries and customer credit.

Module 5: Cross-Border Payments and Currency Handling

Select between dynamic currency conversion (DCC) at gateway or application-level currency conversion based on margin and transparency goals.

Store transaction amounts in both source and settlement currency with exchange rate and timestamp for reconciliation.

Validate BIN country against customer-provided billing country to detect potential fraud or routing issues.

Configure settlement reporting to reconcile with bank statements when payouts occur in different currency than transactions.

Handle refunds in original transaction currency when possible; otherwise, document exchange rate variance policies.

Comply with local reporting requirements (e.g., VAT MOSS for EU digital services) by capturing and validating customer location data.

Module 6: Payouts, Settlement, and Reconciliation

Map settlement batches from gateway reports to individual transactions using batch IDs and timestamps for daily reconciliation.

Automate reconciliation by comparing internal ledger entries with gateway settlement files using checksums and hash validation.

Design payout workflows for marketplaces, including hold periods, fee withholding, and compliance with local payout regulations.

Handle chargeback debits and fee reversals by linking them to original transactions and updating financial ledgers accordingly.

Implement retry logic for failed payout attempts with escalating delays and manual review thresholds.

Generate audit-ready reports that trace funds from customer payment to merchant payout, including all fees and adjustments.

Module 7: High Availability and Operational Resilience

Deploy redundant webhook processors with message queuing (e.g., SQS, Kafka) to prevent loss during processing outages.

Implement circuit breakers on payment API calls to prevent cascading failures during gateway degradation.

Simulate gateway downtime monthly to test failover logic and degraded mode functionality (e.g., offline mode or retry queues).

Monitor transaction success rates with SLOs and alert on deviations indicating integration or provider issues.

Version webhook contracts and maintain backward compatibility during payload schema updates from providers.

Conduct post-mortems for every payment-related incident, focusing on detection time, resolution steps, and prevention measures.

Module 8: Regulatory and Legal Considerations

Implement refund windows and auto-refund logic in line with regional regulations (e.g., 14-day cooling-off in EU).

Obtain explicit customer consent for recurring charges using double-opt-in or documented agreement capture.

Adapt payment flows to comply with local payment methods and mandates (e.g., SEPA Direct Debit, PSD2 SCA).

Retain transaction records for minimum statutory periods (e.g., 5 years in many jurisdictions) with secure archival.

Classify and report suspicious transactions to financial intelligence units when thresholds or patterns trigger AML obligations.

Update terms of service and privacy policies to reflect data sharing with processors and third-party service providers.

Payment Processing in Application Development