```mermaid
sequenceDiagram
    participant Controller
    participant Service
    participant Repository
    participant Domain
    participant Integration

    Controller->>Service: processPayment()
    Service->>Repository: savePayment()
    Repository-->>Service: paymentSaved
    Service-->>Controller: paymentProcessed

    alt External API call
        Service->>Integration: sendPaymentRequest()
        Integration-->>Service: paymentResponse
    end

    opt Within DB transaction
        Service->>Repository: beginTransaction()
        Repository-->>Service: transactionStarted
        Service->>Repository: commitTransaction()
    end
    Note over Service: Success (commit)

    opt External Failure
        Service->>Integration: sendPaymentRequest()
        Integration-->>Service: paymentFailure
        Service->>Repository: rollbackTransaction()
        Repository-->>Service: transactionRolledBack
    end

    opt DB Failure
        Service->>Repository: throwException()
        Repository-->>Service: exceptionOccurred
        Service->>Repository: rollbackTransaction()
        Repository-->>Service: transactionRolledBack
    end
```