Design a donation service for a 3‑day charity

System Design Prompt

You are designing an online donation service for a 3-day charity campaign.

Requirements

• Donors can:
  • Select a charity campaign (single campaign lasting 3 days).
  • Enter donation amount and basic donor info.
  • Pay using a third-party payment provider (e.g., card processor).
  • Receive a confirmation (and optionally a receipt).
• The system must handle:
  • Payment failures (declines, timeouts, provider errors).
  • Retries and idempotency (avoid double-charging/double-recording).
  • High traffic spikes (campaign launches and closing hours).
  • Accurate reporting of total funds raised.

Out of scope (optional, clarify with interviewer)

• Fraud detection, tax receipts, multiple charities, recurring donations, chargebacks.

Deliverables

Describe:

1. APIs and high-level architecture.
2. Data model and key flows (happy path + failure paths).
3. How you ensure correctness (no duplicates) and scalability.
4. Observability and operational considerations.