Description: This flow demonstrates the complete payment process for a registered customer using a previously saved card token. The customer must be identified by customerId during intent creation, which enables card management operations.Key Details:
Authentication: Uses Secret Key for intent creation, Public Key for client-side operations
customerId: Required for saved cards; enables customerToken generation
Card Token: Encrypted stored card reference; requires CVV for each transaction
3DS Flow: Most card transactions redirect to bank's 3D Secure page
Security: CVV is never stored; only provided during confirmation
