Design a 3-day online donation system

System Design: 3-day donation campaign

Design an online donation system for a 3-day fundraising campaign.

Requirements

• Users can donate money to a campaign during the 3-day window.
• Support common payment methods (e.g., credit card, Apple Pay) via a third-party payment processor.
• Show donors a confirmation/receipt.
• Provide an admin/organizer view to track total donations over time.

Scale & reliability assumptions

• Traffic spikes heavily during the final hours (e.g., 100× normal).
• Must not double-charge donors.
• System should tolerate retries/timeouts from clients and the payment provider.

Nice-to-haves (if time)

• Top donors / recent donations feed.
• Fraud/spam prevention.
• Refunds/chargebacks.
• Multi-currency.

Explain APIs, data model, core components, and how you handle consistency, idempotency, and failure modes.