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+```mermaid
+sequenceDiagram
+    participant User
+    participant Controller
+    participant Service
+    participant Repository
+    participant Gateway
+
+    User->>Controller: 결제 요청
+    Controller->>Service: 결제 처리 요청
+    Service->>Repository: 트랜잭션 시작
+    alt 정상 흐름
+        Repository-->>Service: 트랜잭션 ID 반환
+        Service->>Gateway: 결제 요청
+        Gateway-->>Service: 결제 성공
+        Service->>Repository: 트랜잭션 커밋
+        Repository-->>Service: 커밋 성공
+    else 외부 실패
+        Gateway-->>Service: 결제 실패
+        Service->>Repository: 트랜잭션 롤백
+        Repository-->>Service: 롤백 성공
+    else DB 실패
+        Service->>Repository: 트랜잭션 롤백
+        Repository-->>Service: 롤백 실패
+    end
+    Service-->>Controller: 결제 결과 반환
+    Controller-->>User: 결제 결과 응답
+```
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