```mermaid
sequenceDiagram
    participant User
    participant PaymentGateway
    participant PaymentService
    participant Database

    User->>+PaymentService: Start Payment
    PaymentService->>+PaymentGateway: Process Payment
    PaymentGateway-->>-PaymentService: Payment Success
    PaymentService->>Database: Record Payment
    Database-->>-PaymentService: Payment Recorded
    PaymentService-->>-User: Payment Confirmed

    %% External Failure
    User->>+PaymentService: Start Payment
    PaymentService->>+PaymentGateway: Process Payment
    PaymentGateway-->>-PaymentService: Payment Failed
    PaymentService-->>-User: Payment Failed

    %% DB Failure
    User->>+PaymentService: Start Payment
    PaymentService->>+PaymentGateway: Process Payment
    PaymentGateway-->>-PaymentService: Payment Success
    PaymentService->>Database: Record Payment
    Database-->>-PaymentService: DB Failure
    PaymentService-->>-User: Payment Processing Error

    %% Commit/Rollback
    Note over PaymentService: Commit if successful
    Note over PaymentService: Rollback if there's an error
```