diff --git a/internal/service/gameopen/service.go b/internal/service/gameopen/service.go
index 67fb383..f75bc82 100644
--- a/internal/service/gameopen/service.go
+++ b/internal/service/gameopen/service.go
@@ -101,23 +101,26 @@ func (s *GameOpenService) HandleUpdateCoin(ctx context.Context, req UpdateCoinRe
 		s.saveCallbackLog(ctx, "update-coin", rawJSON, resp, credential.SysOrigin, req, &userID, gameOpenLogStatusFailed)
 		return resp
 	}
-	if !exists {
-		if err := s.java.ChangeGoldBalance(ctx, integration.GoldReceiptCommand{
-			ReceiptType:         receiptTypeFromType(req.Type),
-			UserID:              userID,
-			SysOrigin:           credential.SysOrigin,
-			EventID:             eventID,
-			Remark:              fmt.Sprintf("game=%s rewardType=%d round=%s", req.GameID, req.RewardType, req.RoundID),
-			Amount:              integration.NewPennyAmountPayloadFromDollar(req.Coin),
-			CloseDelayAsset:     false,
-			OpUserType:          "APP",
-			CustomizeOrigin:     "GAME_OPEN_" + strings.TrimSpace(req.GameID),
-			CustomizeOriginDesc: "GAME OPEN[" + strings.TrimSpace(req.GameID) + "]",
-		}); err != nil {
-			resp := failResponse(gameOpenCodeServerError, err.Error())
-			s.saveCallbackLog(ctx, "update-coin", rawJSON, resp, credential.SysOrigin, req, &userID, gameOpenLogStatusFailed)
-			return resp
-		}
+	if exists {
+		resp := failResponse(gameOpenCodeDuplicateOrder, "duplicate orderId")
+		s.saveCallbackLog(ctx, "update-coin", rawJSON, resp, credential.SysOrigin, req, &userID, gameOpenLogStatusFailed)
+		return resp
+	}
+	if err := s.java.ChangeGoldBalance(ctx, integration.GoldReceiptCommand{
+		ReceiptType:         receiptTypeFromType(req.Type),
+		UserID:              userID,
+		SysOrigin:           credential.SysOrigin,
+		EventID:             eventID,
+		Remark:              fmt.Sprintf("game=%s rewardType=%d round=%s", req.GameID, req.RewardType, req.RoundID),
+		Amount:              integration.NewPennyAmountPayloadFromDollar(req.Coin),
+		CloseDelayAsset:     false,
+		OpUserType:          "APP",
+		CustomizeOrigin:     "GAME_OPEN_" + strings.TrimSpace(req.GameID),
+		CustomizeOriginDesc: "GAME OPEN[" + strings.TrimSpace(req.GameID) + "]",
+	}); err != nil {
+		resp := failResponse(gameOpenCodeServerError, err.Error())
+		s.saveCallbackLog(ctx, "update-coin", rawJSON, resp, credential.SysOrigin, req, &userID, gameOpenLogStatusFailed)
+		return resp
 	}
 
 	balance, err := s.readUserBalance(ctx, userID)
diff --git a/internal/service/gameopen/service_test.go b/internal/service/gameopen/service_test.go
index 7f8d55b..e615d12 100644
--- a/internal/service/gameopen/service_test.go
+++ b/internal/service/gameopen/service_test.go
@@ -141,6 +141,45 @@ func TestHandleUpdateCoin(t *testing.T) {
 	}
 }
 
+func TestHandleUpdateCoinDuplicateOrderReturns10003(t *testing.T) {
+	gateway := &stubGateway{
+		credential: integration.UserCredential{UserID: 1234567, SysOrigin: "LIKEI"},
+		profile: integration.UserProfile{
+			ID:      1234567,
+			Account: "1234567",
+		},
+		balance: 99,
+		exists:  true,
+	}
+	service := NewGameOpenService(config.Config{
+		GameOpen: config.GameOpenConfig{AppKey: "game-open-test-key"},
+	}, nil, gateway)
+	req := UpdateCoinRequest{
+		OrderID:    "27822d8ba4a34d0e8db3e049716d427d",
+		GameID:     "101",
+		RoundID:    "round-1",
+		UID:        "1234567",
+		Coin:       15,
+		Type:       2,
+		RewardType: 2,
+		Token:      "token",
+		WinID:      "win-1",
+		RoomID:     "room-1",
+	}
+	req.Sign = buildUpdateCoinSign(req, "game-open-test-key")
+
+	resp := service.HandleUpdateCoin(context.Background(), req, "{}")
+	if resp.ErrorCode != gameOpenCodeDuplicateOrder {
+		t.Fatalf("HandleUpdateCoin() errorCode = %d, want %d", resp.ErrorCode, gameOpenCodeDuplicateOrder)
+	}
+	if resp.ErrorMsg != "duplicate orderId" {
+		t.Fatalf("HandleUpdateCoin() errorMsg = %q", resp.ErrorMsg)
+	}
+	if gateway.cmd.EventID != "" {
+		t.Fatalf("HandleUpdateCoin() should not change balance for duplicate order, got event id %q", gateway.cmd.EventID)
+	}
+}
+
 func TestHandleQueryUserAcceptsAccountUID(t *testing.T) {
 	gateway := &stubGateway{
 		credential: integration.UserCredential{UserID: 4569421795454615552, SysOrigin: "LIKEI"},
diff --git a/internal/service/gameopen/types.go b/internal/service/gameopen/types.go
index 7ecb361..7c55910 100644
--- a/internal/service/gameopen/types.go
+++ b/internal/service/gameopen/types.go
@@ -11,6 +11,7 @@ import (
 
 const (
 	gameOpenCodeSuccess        = 0
+	gameOpenCodeDuplicateOrder = 10003
 	gameOpenCodeBadRequest     = 4001
 	gameOpenCodeSignatureError = 4002
 	gameOpenCodeTokenInvalid   = 4003