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.