diff --git a/docs/architecture/transaction-sequence.md b/docs/architecture/transaction-sequence.md
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+sequenceDiagram
+    participant User
+    participant Controller
+    participant Service
+    participant Repository
+    participant ExternalGateway
+
+    User->>Controller: 결제 요청
+    Controller->>Service: 결제 처리 요청
+    Service->>Repository: 트랜잭션 시작
+    Service->>ExternalGateway: 결제 요청
+    alt 결제 성공
+        ExternalGateway-->>Service: 결제 성공 응답
+        Service->>Repository: 트랜잭션 커밋
+        Repository-->>Service: 커밋 완료
+        Service-->>Controller: 결제 완료 응답
+        Controller-->>User: 결제 완료
+    else 외부 실패
+        ExternalGateway-->>Service: 결제 실패 응답
+        Service->>Repository: 트랜잭션 롤백
+        Repository-->>Service: 롤백 완료
+        Service-->>Controller: 결제 실패 응답
+        Controller-->>User: 결제 실패
+    else DB 실패
+        Service->>Repository: 트랜잭션 롤백
+        Repository-->>Service: 롤백 완료
+        Service-->>Controller: DB 오류 응답
+        Controller-->>User: DB 오류
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