Design an Online Payment System like PayPal

Functional Requirements:

• Users can register, log in, and manage their accounts.
• Users can add and verify payment methods (e.g., credit card, bank account).
• Users can send payments to other users using email or username.
• Users can receive payments and withdraw funds to their bank accounts.
• Users can view their transaction history and current balance.
• The system must process transactions securely and reliably.
• Admins can monitor transactions and manage user accounts for compliance.

Non-Functional Requirements:

• Security: All sensitive data must be encrypted in transit and at rest. The system should have fraud detection and prevention mechanisms.
• Availability: The system should be highly available, targeting 99.9% uptime.
• Scalability: The system should handle growth in users and transaction volume.
• Performance: Transactions should be processed within a few seconds.
• Reliability: The system must ensure no loss or duplication of transactions.
• Compliance: The system must comply with relevant financial regulations (e.g., KYC, AML).
• Usability: The user interface should be simple and intuitive for both web and mobile clients.