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+```mermaid
+sequenceDiagram
+    participant User
+    participant Controller
+    participant Service
+    participant Repository
+    participant ExternalGateway
+
+    User->>Controller: 결제 요청
+    Controller->>Service: 결제 처리 요청
+    Service->>Repository: 결제 정보 저장
+    Repository-->>Service: 저장 완료
+    Service->>ExternalGateway: 결제 요청
+    ExternalGateway-->>Service: 결제 성공
+    Service-->>Controller: 결제 완료
+    Controller-->>User: 결제 성공 응답
+
+    Note over Service: DB 실패 시
+    Service->>Repository: 롤백 요청
+    Repository-->>Service: 롤백 완료
+    Service-->>Controller: 결제 실패
+    Controller-->>User: 결제 실패 응답
+
+    Note over Service: 외부 실패 시
+    Service->>Controller: 결제 실패
+    Controller-->>User: 결제 실패 응답
+```
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