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+```mermaid
+sequenceDiagram
+    participant User as 사용자
+    participant PaymentGateway as 결제 게이트웨이
+    participant Banking as 은행
+    participant System as 시스템
+
+    User->>System: 결제 요청
+    activate System
+    System->>PaymentGateway: 결제 처리 요청
+    activate PaymentGateway
+
+    alt 성공
+        PaymentGateway-->>System: 결제 성공
+        activate System
+        System->>Banking: 금액 이체 요청
+        activate Banking
+        Banking-->>System: 이체 성공
+        deactivate Banking
+        System-->>User: 결제 완료
+        deactivate System
+    else 외부 실패
+        PaymentGateway-->>System: 결제 실패
+        deactivate PaymentGateway
+        System-->>User: 결제 실패 메시지
+        deactivate System
+    else DB 실패
+        PaymentGateway-->>System: 결제 처리 중 오류 발생
+        deactivate PaymentGateway
+        System->>System: 롤백 처리
+        System-->>User: 결제 처리 실패 및 복원
+        deactivate System
+    end
+
+    deactivate PaymentGateway
+    deactivate System
+```
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