diff --git a/app/src/main/java/com/unibuy/smartdevice/service/MqttService.java b/app/src/main/java/com/unibuy/smartdevice/service/MqttService.java
index 8951aa9..0fe7b03 100644
--- a/app/src/main/java/com/unibuy/smartdevice/service/MqttService.java
+++ b/app/src/main/java/com/unibuy/smartdevice/service/MqttService.java
@@ -136,6 +136,89 @@ public class MqttService extends Service {
                             Log.e(TAG, "NFC checkout failed: " + e.getMessage());
                             mqttManager.publishCommandAck(cmdId, "failed", "NFC checkout failed: " + e.getMessage());
                         }
+                    } else if ("change".equals(cmd)) {
+                        Log.i(TAG, "Executing remote change command...");
+                        try {
+                            int amount = 0;
+                            if (command.getPayload() != null && command.getPayload().isJsonObject()) {
+                                com.google.gson.JsonObject payloadObj = command.getPayload().getAsJsonObject();
+                                if (payloadObj.has("amount")) {
+                                    amount = payloadObj.get("amount").getAsInt();
+                                }
+                            }
+
+                            if (amount <= 0) {
+                                throw new Exception("Invalid or missing amount: " + amount);
+                            }
+
+                            int finalAmount = amount;
+                            com.unibuy.smartdevice.tools.CashPayoutManager payoutManager = new com.unibuy.smartdevice.tools.CashPayoutManager(getApplicationContext(), new com.unibuy.smartdevice.tools.CashPayoutManager.PayoutListener() {
+                                @Override
+                                public void onProgress(String message) {
+                                    Log.d(TAG, "Payout Progress: " + message);
+                                }
+
+                                @Override
+                                public void onSuccess() {
+                                    Log.i(TAG, "Remote payout success for amount: " + finalAmount);
+                                    mqttManager.publishCommandAck(cmdId, "success", "Payout completed: " + finalAmount);
+                                }
+
+                                @Override
+                                public void onFailure(String error) {
+                                    Log.e(TAG, "Remote payout failed: " + error);
+                                    mqttManager.publishCommandAck(cmdId, "failed", "Payout failed: " + error);
+                                }
+                            });
+
+                            payoutManager.startPayout(amount);
+                            // 注意：ACK 會在 PayoutListener 的回調中發送，不在此處發送。
+                        } catch (Exception e) {
+                            Log.e(TAG, "Failed to parse or start change command: " + e.getMessage());
+                            mqttManager.publishCommandAck(cmdId, "failed", "Error: " + e.getMessage());
+                        }
+                    } else if ("dispense".equals(cmd)) {
+                        Log.i(TAG, "Executing remote dispense command...");
+                        try {
+                            int slot = -1;
+                            if (command.getPayload() != null && command.getPayload().isJsonObject()) {
+                                com.google.gson.JsonObject payloadObj = command.getPayload().getAsJsonObject();
+                                if (payloadObj.has("slot_no")) {
+                                    slot = payloadObj.get("slot_no").getAsInt();
+                                } else if (payloadObj.has("slot")) {
+                                    slot = payloadObj.get("slot").getAsInt();
+                                }
+                            }
+
+                            if (slot <= 0) {
+                                throw new Exception("Invalid or missing slot_no: " + slot);
+                            }
+
+                            int finalSlot = slot;
+                            com.unibuy.smartdevice.tools.ProductDispenseManager dispenseManager = new com.unibuy.smartdevice.tools.ProductDispenseManager(getApplicationContext(), new com.unibuy.smartdevice.tools.ProductDispenseManager.DispenseListener() {
+                                @Override
+                                public void onProgress(String message) {
+                                    Log.d(TAG, "Dispense Progress: " + message);
+                                }
+
+                                @Override
+                                public void onSuccess() {
+                                    Log.i(TAG, "Remote dispense success for slot: " + finalSlot);
+                                    mqttManager.publishCommandAck(cmdId, "success", "Product dispensed from slot: " + finalSlot);
+                                }
+
+                                @Override
+                                public void onFailure(String error) {
+                                    Log.e(TAG, "Remote dispense failed: " + error);
+                                    mqttManager.publishCommandAck(cmdId, "failed", "Dispense failed: " + error);
+                                }
+                            });
+
+                            dispenseManager.startDispense(slot);
+                        } catch (Exception e) {
+                            Log.e(TAG, "Failed to parse or start dispense command: " + e.getMessage());
+                            mqttManager.publishCommandAck(cmdId, "failed", "Error: " + e.getMessage());
+                        }
                     } else {
                         Log.w(TAG, "Unknown MQTT command: " + cmd);
                         mqttManager.publishCommandAck(cmdId, "failed", "Unknown command");
diff --git a/app/src/main/java/com/unibuy/smartdevice/tools/CashPayoutManager.java b/app/src/main/java/com/unibuy/smartdevice/tools/CashPayoutManager.java
new file mode 100644
index 0000000..ececb4e
--- /dev/null
+++ b/app/src/main/java/com/unibuy/smartdevice/tools/CashPayoutManager.java
@@ -0,0 +1,235 @@
+package com.unibuy.smartdevice.tools;
+
+import android.content.Context;
+import android.os.Handler;
+import android.os.Looper;
+import android.util.Log;
+
+import com.unibuy.smartdevice.exception.ErrorCode;
+import com.unibuy.smartdevice.tools.SimpleCashAcceptorHandler;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 遠端找零管理器
+ * 負責處理 MDB 設備的連線、初始化、庫存查詢及退幣/退鈔指令發送。
+ */
+public class CashPayoutManager {
+    private static final String TAG = "CashPayoutManager";
+
+    public interface PayoutListener {
+        void onProgress(String message);
+        void onSuccess();
+        void onFailure(String error);
+    }
+
+    private final Context context;
+    private final PayoutListener listener;
+    private SimpleCashAcceptorHandler handler;
+    private final Handler mainHandler = new Handler(Looper.getMainLooper());
+
+    // 庫存變數
+    private int coin50_count = 0;
+    private int coin10_count = 0;
+    private int coin5_count = 0;
+    private int coin1_count = 0;
+    private int note100_count = 0;
+
+    public CashPayoutManager(Context context, PayoutListener listener) {
+        this.context = context;
+        this.listener = listener;
+    }
+
+    public void startPayout(int amount) {
+        Log.i(TAG, "Starting remote payout for amount: " + amount);
+        listener.onProgress("正在初始化退幣系統...");
+
+        handler = new SimpleCashAcceptorHandler(context, event -> {
+            Log.d(TAG, "MDB Event: " + event);
+            handleMdbEvent(event);
+        });
+
+        new Thread(() -> {
+            String connectResult = handler.connect();
+            if ("成功連接到 USB 轉接器！".equals(connectResult)) {
+                mainHandler.post(() -> {
+                    handler.startReading();
+                    performInitializationSequence(amount);
+                });
+            } else {
+                mainHandler.post(() -> listener.onFailure("MDB 連線失敗: " + connectResult));
+            }
+        }).start();
+    }
+
+    private void performInitializationSequence(int amount) {
+        // 依序發送初始化與查詢指令
+        // 指令序列參考 CashMachineSettings 與 CashPayDialog
+        sendMdbCommand("0C00000000", 0, () -> { // 先禁止硬幣接收
+        sendMdbCommand("3400000000", 500, () -> { // 禁止紙鈔接收
+        sendMdbCommand("370100000002", 500, () -> { // 設定紙鈔類型
+        sendMdbCommand("3703", 500, () -> { // 查詢設置
+        sendMdbCommand("3705", 500, () -> { // 查詢紙鈔庫存
+        sendMdbCommand("0A", 1000, () -> { // 查詢硬幣庫存
+            calculateAndExecutePayout(amount);
+        });});});});});});
+    }
+
+    private void calculateAndExecutePayout(int amount) {
+        listener.onProgress("正在計算退幣組合...");
+        List<ChangeCommand> commands = new ArrayList<>();
+        int remaining = amount;
+
+        // 1. 100元紙鈔
+        int hundredsToGive = Math.min(remaining / 100, note100_count);
+        if (hundredsToGive > 0) {
+            String cmd = "370600000" + String.format("%01X", hundredsToGive);
+            commands.add(new ChangeCommand(cmd, 100, hundredsToGive));
+            remaining -= hundredsToGive * 100;
+        }
+
+        // 2. 50元硬幣
+        int fiftiesToGive = Math.min(remaining / 50, coin50_count);
+        if (fiftiesToGive > 0) {
+            String cmd = "0D" + String.format("%01X", fiftiesToGive) + "4";
+            commands.add(new ChangeCommand(cmd, 50, fiftiesToGive));
+            remaining -= fiftiesToGive * 50;
+        }
+
+        // 3. 10元硬幣
+        int tensToGive = Math.min(remaining / 10, coin10_count);
+        if (tensToGive > 0) {
+            String cmd = "0D" + String.format("%01X", tensToGive) + "2";
+            commands.add(new ChangeCommand(cmd, 10, tensToGive));
+            remaining -= tensToGive * 10;
+        }
+
+        // 4. 5元硬幣
+        int fivesToGive = Math.min(remaining / 5, coin5_count);
+        if (fivesToGive > 0) {
+            String cmd = "0D" + String.format("%01X", fivesToGive) + "1";
+            commands.add(new ChangeCommand(cmd, 5, fivesToGive));
+            remaining -= fivesToGive * 5;
+        }
+
+        // 5. 1元硬幣
+        int onesToGive = Math.min(remaining, coin1_count);
+        if (onesToGive > 0) {
+            String cmd = "0D" + String.format("%01X", onesToGive) + "0";
+            commands.add(new ChangeCommand(cmd, 1, onesToGive));
+            remaining -= onesToGive;
+        }
+
+        if (remaining > 0) {
+            Log.w(TAG, "Insufficient inventory to payout full amount. Missing: " + remaining);
+            // 依然執行現有的，但回報錯誤訊息
+        }
+
+        if (commands.isEmpty()) {
+            listener.onFailure("無需找零或庫存不足以找零");
+            close();
+            return;
+        }
+
+        executePayoutCommands(commands, 0);
+    }
+
+    private void executePayoutCommands(List<ChangeCommand> commands, int index) {
+        if (index >= commands.size()) {
+            listener.onProgress("退幣完成");
+            // 延遲關閉，確保指令處理完畢
+            mainHandler.postDelayed(() -> {
+                close();
+                listener.onSuccess();
+            }, 2000);
+            return;
+        }
+
+        ChangeCommand current = commands.get(index);
+        listener.onProgress("正在執行: " + current.denomination + "元 x " + current.count);
+        
+        sendMdbCommand(current.command, 0, () -> {
+            // 退幣指令後需要較長延遲
+            executePayoutCommands(commands, index + 1);
+        });
+    }
+
+    private void sendMdbCommand(String hexCommand, int delay, Runnable onComplete) {
+        mainHandler.postDelayed(() -> {
+            new Thread(() -> {
+                try {
+                    byte[] command = hexStringToByteArray(hexCommand);
+                    handler.writeData(command);
+                    if (onComplete != null) {
+                        mainHandler.post(onComplete);
+                    }
+                } catch (Exception e) {
+                    Log.e(TAG, "Error sending MDB command: " + hexCommand, e);
+                }
+            }).start();
+        }, Math.max(delay, 1000)); // 每個指令至少間隔 1 秒，退幣可能需要更長
+    }
+
+    private void handleMdbEvent(String event) {
+        if (event == null || event.trim().isEmpty()) return;
+        String[] parts = event.trim().split("\\s+");
+
+        // 解析硬幣庫存 (0A 回傳)
+        if (parts.length == 19) {
+            try {
+                coin1_count = Integer.parseInt(parts[2], 16);
+                coin5_count = Integer.parseInt(parts[3], 16);
+                coin10_count = Integer.parseInt(parts[4], 16);
+                coin50_count = Integer.parseInt(parts[6], 16);
+                Log.d(TAG, String.format("Inventory Update: 1=%d, 5=%d, 10=%d, 50=%d", 
+                    coin1_count, coin5_count, coin10_count, coin50_count));
+            } catch (Exception e) {
+                Log.e(TAG, "Parse coin inventory error", e);
+            }
+        }
+
+        // 解析百鈔庫存 (3705 回傳)
+        if (parts.length >= 30) {
+            try {
+                int noteCount = Integer.parseInt(parts[3], 16);
+                if (noteCount >= 0 && noteCount <= 100) {
+                    note100_count = noteCount;
+                    Log.d(TAG, "Inventory Update: 100=" + note100_count);
+                }
+            } catch (Exception e) {
+                Log.e(TAG, "Parse bill inventory error", e);
+            }
+        }
+    }
+
+    private void close() {
+        if (handler != null) {
+            handler.stopReading();
+            handler.close();
+            handler = null;
+        }
+    }
+
+    private byte[] hexStringToByteArray(String s) {
+        int len = s.length();
+        byte[] data = new byte[len / 2];
+        for (int i = 0; i < len; i += 2) {
+            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+                    + Character.digit(s.charAt(i + 1), 16));
+        }
+        return data;
+    }
+
+    private static class ChangeCommand {
+        final String command;
+        final int denomination;
+        final int count;
+
+        ChangeCommand(String command, int denomination, int count) {
+            this.command = command;
+            this.denomination = denomination;
+            this.count = count;
+        }
+    }
+}
diff --git a/app/src/main/java/com/unibuy/smartdevice/tools/ProductDispenseManager.java b/app/src/main/java/com/unibuy/smartdevice/tools/ProductDispenseManager.java
new file mode 100644
index 0000000..4f6fbca
--- /dev/null
+++ b/app/src/main/java/com/unibuy/smartdevice/tools/ProductDispenseManager.java
@@ -0,0 +1,175 @@
+package com.unibuy.smartdevice.tools;
+
+import android.content.Context;
+import android.os.Handler;
+import android.os.Looper;
+import android.util.Log;
+
+import com.unibuy.smartdevice.MyApp;
+import com.unibuy.smartdevice.controller.DevController;
+import com.unibuy.smartdevice.controller.DevXinYuanController;
+import com.unibuy.smartdevice.devices.PortTools;
+
+/**
+ * 遠端出貨管理器
+ * 負責在背景執行商品出貨流程，不依賴於 UI (DispatchDialog)。
+ */
+public class ProductDispenseManager {
+    private static final String TAG = "ProductDispenseManager";
+
+    public interface DispenseListener {
+        void onProgress(String message);
+        void onSuccess();
+        void onFailure(String error);
+    }
+
+    private final Context context;
+    private final DispenseListener listener;
+    private final Handler mainHandler = new Handler(Looper.getMainLooper());
+    private int checkRetryCount = 0;
+
+    public ProductDispenseManager(Context context, DispenseListener listener) {
+        this.context = context;
+        this.listener = listener;
+    }
+
+    public void startDispense(int slot) {
+        Log.i(TAG, "Starting background dispense for slot: " + slot);
+        listener.onProgress("正在檢查貨道狀態...");
+
+        DevXinYuanController controller = MyApp.getInstance().getDevXinYuanController();
+        if (controller == null || !controller.isConnected()) {
+            listener.onFailure("下位機控制器未連線");
+            return;
+        }
+
+        // 步驟 1: 檢查貨道狀態 (CMD 01 -> VMC 02)
+        controller.getReadBufferByNow(new DevController.ReadBufferOnScheduler(new HandlerMain(context, null) {
+            @Override
+            protected void execute(Context context, int commandCode, String message) {}
+        }) {
+            @Override
+            protected HandlerMain setHandlerMain() { return getSrcHandlerMain(); }
+            @Override
+            protected Class<?> setCls() { return getClass(); }
+
+            @Override
+            public void readBufferOnScheduler(DevController devController, HandlerMain handlerMain) {
+                boolean isCMD = false;
+                boolean isStatusOk = false;
+
+                for (byte[] buffer : devController.getReadBufferByMax()) {
+                    if (buffer[0] == 0x02) { // VMC_02_CHECK_SLOT_STATUS
+                        isCMD = true;
+                        Log.d(TAG, "Check Slot Result: " + PortTools.showHex(buffer));
+                        // 01: OK, 02: PDT_EMPTY (有些機型空也會允許出貨指令), 04: TMP_USE
+                        if (buffer[1] == 0x01 || buffer[1] == 0x02 || buffer[1] == 0x04) {
+                            isStatusOk = true;
+                        }
+                        break;
+                    }
+                }
+
+                if (isCMD) {
+                    if (isStatusOk) {
+                        mainHandler.post(() -> executeActualDispense(slot));
+                    } else {
+                        mainHandler.post(() -> listener.onFailure("貨道狀態異常，無法出貨"));
+                    }
+                } else {
+                    if (checkRetryCount < 3) {
+                        checkRetryCount++;
+                        controller.addSendBuffer(controller.getDevXinYuan().checkSlot(slot));
+                        controller.getReadBufferByNow(this, 1000);
+                    } else {
+                        mainHandler.post(() -> listener.onFailure("下位機檢查貨道無回應"));
+                    }
+                }
+            }
+        }, 1000);
+
+        controller.addSendBuffer(controller.getDevXinYuan().checkSlot(slot));
+    }
+
+    private void executeActualDispense(int slot) {
+        listener.onProgress("貨道正常，正在發送出貨指令...");
+        DevXinYuanController controller = MyApp.getInstance().getDevXinYuanController();
+
+        // 步驟 2: 發送出貨指令並監聽狀態 (CMD 06 -> VMC 04)
+        controller.getReadBufferByNow(new DevController.ReadBufferOnScheduler(new HandlerMain(context, null) {
+            @Override
+            protected void execute(Context context, int commandCode, String message) {}
+        }) {
+            @Override
+            protected HandlerMain setHandlerMain() { return getSrcHandlerMain(); }
+            @Override
+            protected Class<?> setCls() { return getClass(); }
+
+            @Override
+            public void readBufferOnScheduler(DevController devController, HandlerMain handlerMain) {
+                boolean isCMD = false;
+                boolean isSuccess = false;
+                boolean isFailed = false;
+                String errorDetail = "";
+
+                for (byte[] buffer : devController.getReadBufferByMax()) {
+                    if (buffer[0] == 0x04) { // VMC_04_BUY_STATUS
+                        isCMD = true;
+                        Log.d(TAG, "Dispense Status: " + PortTools.showHex(buffer));
+                        
+                        // 02: OK, 24: PLIS_BOX (可能是某些特定機型的成功代碼)
+                        if (buffer[1] == 0x02 || buffer[1] == 0x24) {
+                            isSuccess = true;
+                            break;
+                        } 
+                        // 01: NOW (處理中), 10: PLATFORM_UP, 11: PLATFORM_DOWN
+                        else if (buffer[1] == 0x01 || buffer[1] == 0x10 || buffer[1] == 0x11) {
+                            continue;
+                        } 
+                        else {
+                            isFailed = true;
+                            errorDetail = String.format("%02X", buffer[1]);
+                        }
+                    }
+                }
+
+                if (isSuccess) {
+                    mainHandler.post(() -> {
+                        updateLocalStock(slot);
+                        listener.onSuccess();
+                    });
+                } else if (isFailed) {
+                    String finalErrorDetail = errorDetail;
+                    mainHandler.post(() -> listener.onFailure("出貨失敗，錯誤代碼: " + finalErrorDetail));
+                } else {
+                    // 繼續輪詢直到成功或失敗
+                    controller.getReadBufferByNow(this, 1000);
+                }
+            }
+        }, 1000);
+
+        controller.addSendBuffer(controller.getDevXinYuan().getProduct(slot));
+    }
+
+    private void updateLocalStock(int slot) {
+        try {
+            // 預設為 VMC 貨道 (Field 1)
+            int field = com.unibuy.smartdevice.devices.SlotField.VMC.getField();
+            com.unibuy.smartdevice.structure.SlotStructure slotData = MyApp.getInstance().getSlotData(field, slot);
+            int currentCount = slotData.getCount();
+            if (currentCount > 0) {
+                int newCount = currentCount - 1;
+                slotData.setCount(newCount);
+                Log.i(TAG, "Updated slot " + slot + " count: " + currentCount + " -> " + newCount);
+                
+                // 儲存至資料庫
+                com.unibuy.smartdevice.database.SlotsDao slotsDao = new com.unibuy.smartdevice.database.SlotsDao(context);
+                slotsDao.deleteAll();
+                slotsDao.insertAll(MyApp.getInstance().getSlotMap());
+                slotsDao.close();
+            }
+        } catch (Exception e) {
+            Log.e(TAG, "Failed to update local stock: " + e.getMessage());
+        }
+    }
+}