```mermaid
sequenceDiagram
    participant User
    participant PaymentGateway
    participant Application
    participant Database
    User->>Application: Initiate Payment
    Application->>PaymentGateway: Process Payment
    alt Successful Payment
        PaymentGateway-->>Application: Payment Approved
        Application->>Database: Commit Transaction
        Database-->>Application: Transaction Committed
        Application-->>User: Payment Successful
    else External Failure
        PaymentGateway-->>Application: Payment Error
        Application-->>User: Payment Failed
    else DB Failure
        Application->>Database: Attempt Transaction
        Database-->>Application: Transaction Error
        Application->>Database: Rollback Transaction
        Database-->>Application: Transaction Rolled Back
        Application-->>User: Payment Failed
    end
```