diff --git a/Assets/PerfectWorld/Scripts/Managers/EC_Inventory.cs b/Assets/PerfectWorld/Scripts/Managers/EC_Inventory.cs
index 7d113a8309..cb5a5fde1c 100644
--- a/Assets/PerfectWorld/Scripts/Managers/EC_Inventory.cs
+++ b/Assets/PerfectWorld/Scripts/Managers/EC_Inventory.cs
@@ -159,6 +159,7 @@ namespace BrewMonster.Scripts.Managers
             return true;
         }
 
+        /// <summary>C++ <c>CECInventory::MergeItem</c>: walk slots, call <c>CECIvtrItem::MergeItem</c>, then new slot if needed.</summary>
         public bool MergeItem(int tid, int iExpireDate, int iAmount, out int piLastSlot, out int piLastAmount)
         {
             piLastSlot = -1;
@@ -171,16 +172,8 @@ namespace BrewMonster.Scripts.Managers
                 var slotItem = m_aItems[i];
                 if (slotItem != null)
                 {
-                    if (slotItem.GetTemplateID() != tid)
-                        continue;
-
-                    int pileLimit = Math.Max(1, EC_IvtrItem.GetPileLimit(tid));
-                    int canAdd = Math.Max(0, pileLimit - Math.Max(0, slotItem.GetCount()));
-                    if (canAdd <= 0) continue;
-
-                    int add = Math.Min(canAdd, iAmount);
-                    slotItem.AddAmount(add);
-                    iAmount -= add;
+                    int iNumMerge = slotItem.MergeItem(tid, iAmount);
+                    iAmount -= iNumMerge;
 
                     if (iAmount == 0)
                     {
diff --git a/Assets/PerfectWorld/Scripts/Managers/EC_InventoryUI.cs b/Assets/PerfectWorld/Scripts/Managers/EC_InventoryUI.cs
index 8a3e9d53e7..cba791e16e 100644
--- a/Assets/PerfectWorld/Scripts/Managers/EC_InventoryUI.cs
+++ b/Assets/PerfectWorld/Scripts/Managers/EC_InventoryUI.cs
@@ -873,6 +873,23 @@ namespace BrewMonster.Scripts.Managers
                 }
             }
 
+            /// <summary>
+            /// Stack count label under slot buttons: prefabs use <c>text_quatity</c> (typo) or <c>text_quantity</c>; legacy code used <c>text_quality</c>.
+            /// Only checks immediate children (Unity <see cref="Transform.Find"/>); deeper layouts fall back to <see cref="Component.GetComponentInChildren{T}"/> below.
+            /// </summary>
+            private static Transform FindStackCountTextTransform(Transform root)
+            {
+                if (root == null) return null;
+                string[] names = { "text_quality", "text_quatity", "text_quantity" };
+                for (int n = 0; n < names.Length; n++)
+                {
+                    var t = root.Find(names[n]);
+                    if (t != null) return t;
+                }
+
+                return null;
+            }
+
             /// <summary>
             /// Update or create text component to show item count on the button
             /// </summary>
@@ -885,22 +902,19 @@ namespace BrewMonster.Scripts.Managers
                 TMPro.TextMeshProUGUI tmpText = null;
                 Text legacyText = null;
 
-                // Find text component
-                var textTransform = button.transform.Find("text_quality");
+                var textTransform = FindStackCountTextTransform(button.transform);
 
                 if (textTransform != null)
                 {
                     tmpText = textTransform.GetComponent<TMPro.TextMeshProUGUI>();
                     legacyText = textTransform.GetComponent<Text>();
                 }
-                else
+
+                if (tmpText == null && legacyText == null)
                 {
-                    // Fallback: find any text in children
                     tmpText = button.GetComponentInChildren<TMPro.TextMeshProUGUI>();
                     if (tmpText == null)
-                    {
                         legacyText = button.GetComponentInChildren<Text>();
-                    }
                 }
 
                 // Update text
diff --git a/Assets/PerfectWorld/Scripts/Managers/EC_IvtrItem/EC_IvtrItem.cs b/Assets/PerfectWorld/Scripts/Managers/EC_IvtrItem/EC_IvtrItem.cs
index 8498617bb8..2314b84926 100644
--- a/Assets/PerfectWorld/Scripts/Managers/EC_IvtrItem/EC_IvtrItem.cs
+++ b/Assets/PerfectWorld/Scripts/Managers/EC_IvtrItem/EC_IvtrItem.cs
@@ -1211,14 +1211,12 @@ namespace BrewMonster.Scripts.Managers
             return iNumAdd;
         }
 
-        /// <summary>Add item amount. Returns new amount of item.</summary>
+        /// <summary>Add item amount. Returns new count (C++ <c>a_Clamp</c> to <c>m_iPileLimit</c>).</summary>
         public int AddAmount(int iAmount)
         {
-            Debug.Log($"[EC_IvtrItem] Old Amount: {m_iCount}");
             m_iCount += iAmount;
             if (m_iCount < 0) m_iCount = 0;
-            //if (m_iCount > m_iPileLimit) m_iCount = m_iPileLimit;
-            Debug.Log($"[EC_IvtrItem] New Amount: {m_iCount}");
+            if (m_iCount > m_iPileLimit) m_iCount = m_iPileLimit;
             return m_iCount;
         }
 
diff --git a/Assets/Scripts/CECHostPlayer.ConfigData.cs b/Assets/Scripts/CECHostPlayer.ConfigData.cs
index bd840e76df..27c715023d 100644
--- a/Assets/Scripts/CECHostPlayer.ConfigData.cs
+++ b/Assets/Scripts/CECHostPlayer.ConfigData.cs
@@ -482,6 +482,47 @@ namespace BrewMonster
                 }
             }
         }
+
+        /// <summary>C++ CECDealInventory::GetItemIndexByFlag</summary>
+        public int GetItemIndexByFlag(int iFlag)
+        {
+            int n = GetSize();
+            for (int i = 0; i < n; i++)
+            {
+                if (GetItem(i, false) != null && m_aItemInfo[i].iFlag == iFlag)
+                    return i;
+            }
+            return -1;
+        }
+
+        /// <summary>C++ CECDealInventory::RemoveItemByFlag</summary>
+        public void RemoveItemByFlag(int iFlag, int iAmount)
+        {
+            int n = GetSize();
+            for (int i = 0; i < n; i++)
+            {
+                var slotItem = GetItem(i, false);
+                if (slotItem == null)
+                    continue;
+
+                var info = m_aItemInfo[i];
+                if (info.iFlag != iFlag)
+                    continue;
+
+                if (iAmount < 0 || iAmount >= info.iAmount)
+                {
+                    SetItem(i, null);
+                }
+                else
+                {
+                    info.iAmount -= iAmount;
+                    m_aItemInfo[i] = info;
+                    if (info.bDelete)
+                        slotItem.AddAmount(-iAmount);
+                }
+                return;
+            }
+        }
     }
     
     //  ��̯��Ʊ�Զ�ת��
diff --git a/Assets/Scripts/CECHostPlayer.Inventory.cs b/Assets/Scripts/CECHostPlayer.Inventory.cs
index 2d383f5e3b..83c2c72450 100644
--- a/Assets/Scripts/CECHostPlayer.Inventory.cs
+++ b/Assets/Scripts/CECHostPlayer.Inventory.cs
@@ -594,7 +594,13 @@ namespace BrewMonster
             UpdateEquipSkins();
         }
 
-        /// <summary>Buy from NPC/booth: server sends PURCHASE_ITEM (cmd_purchase_item). C++ OnMsgHstPurchaseItems.</summary>
+        /// <summary>
+        /// Buy from NPC/booth: S2C PURCHASE_ITEM (<c>cmd_purchase_item</c>).
+        /// Port of <c>CECHostPlayer::OnMsgHstPurchaseItems</c> (EC_HostMsg.cpp): prefer <c>MergeItem</c> like the C++ client.
+        /// If merge lands on a different slot than <c>inv_index</c> (common when stacking into an earlier pile), we still accept
+        /// the merged slot—the strict C++ <c>iLastSlot == inv_index</c> check would skip updates and break buy/stack UI here.
+        /// Fallback: <c>PutItemInSlot(inv_index)</c> then <c>MergeItem</c> when merge alone fails.
+        /// </summary>
         public void OnMsgHstPurchaseItems(ECMSG Msg)
         {
             var data = Msg.dwParam1 as byte[];
@@ -609,6 +615,7 @@ namespace BrewMonster
                 return;
 
             var slotsNeedingDetail = new System.Collections.Generic.List<byte>();
+            bool purchaseSlotMismatch = false;
 
             for (int i = 0; i < header.item_count && index + itemSize <= data.Length; i++)
             {
@@ -616,37 +623,58 @@ namespace BrewMonster
                 int expire_date = BitConverter.ToInt32(data, index); index += 4;
                 int count = (int)BitConverter.ToUInt32(data, index); index += 4;
                 ushort inv_index = BitConverter.ToUInt16(data, index); index += 2;
-                index += 1; // booth_slot
+                byte booth_slot = data[index];
+                index += 1;
 
                 if (inv_index >= pPack.GetSize())
                     pPack.Resize(inv_index + 1);
 
-                bool placed = pPack.PutItemInSlot(inv_index, item_id, expire_date, count, out int lastSlot, out int slotNum);
+                int iLastSlot = 0;
+                int iSlotNum = 0;
+                bool placed = pPack.MergeItem(item_id, expire_date, count, out iLastSlot, out iSlotNum);
+                if (!placed)
+                    placed = pPack.PutItemInSlot(inv_index, item_id, expire_date, count, out iLastSlot, out iSlotNum);
+                if (!placed)
+                    placed = pPack.MergeItem(item_id, expire_date, count, out iLastSlot, out iSlotNum);
                 if (!placed)
                 {
-                    placed = pPack.MergeItem(item_id, expire_date, count, out lastSlot, out slotNum);
-                    if (!placed || lastSlot != inv_index)
-                        continue;
+#if UNITY_EDITOR
+                    UnityEngine.Debug.LogWarning(
+                        $"[OnMsgHstPurchaseItems] Could not place purchase tid={item_id} count={count} inv_index={inv_index}");
+#endif
+                    continue;
                 }
 
-                var pItem = pPack.GetItem(inv_index, false);
+                if (iLastSlot != inv_index)
+                    purchaseSlotMismatch = true;
+
+#if UNITY_EDITOR
+                if (iLastSlot != inv_index)
+                {
+                    UnityEngine.Debug.Log(
+                        $"[OnMsgHstPurchaseItems] Using merge slot {iLastSlot} (packet inv_index={inv_index}) tid={item_id}");
+                }
+#endif
+
+                var pItem = pPack.GetItem(iLastSlot, false);
                 if (pItem != null)
                 {
                     pItem.Package = (byte)Inventory_type.IVTRTYPE_PACK;
-                    pItem.Slot = inv_index;
-                    int cid = pItem.GetClassID();
-                    if (pItem.IsEquipment() ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_TASKNMMATTER ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_TASKDICE ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_TASKITEM ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_GOBLIN_EXPPILL ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_WEDDINGBOOKCARD ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_WEDDINGINVITECARD ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_SKILLTOME ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_GOBLIN ||
-                        cid == (int)EC_IvtrItem.InventoryClassId.ICID_PETEGG)
+                    pItem.Slot = iLastSlot;
+                    // Keep stack size in sync with MergeItem/PutItemInSlot totals (authoritative for this slot).
+                    if (iSlotNum > 0)
+                        pItem.SetCount(iSlotNum);
+                    if (pItem.IsEquipment())
+                        slotsNeedingDetail.Add((byte)iLastSlot);
+                }
+
+                if (header.flag != 0 && GetBoothState() == 2)
+                {
+                    var boothBPack = GetBoothBuyPack();
+                    if (boothBPack != null)
                     {
-                        slotsNeedingDetail.Add((byte)inv_index);
+                        // C++: CDlgInfo FIXMSG_BOOTHBUY — no matching in-game UI hook here; update booth pack only.
+                        boothBPack.RemoveItemByFlag(booth_slot, count);
                     }
                 }
             }
@@ -656,8 +684,18 @@ namespace BrewMonster
             foreach (byte slot in slotsNeedingDetail)
                 UnityGameSession.c2s_CmdGetItemInfo((byte)Inventory_type.IVTRTYPE_PACK, slot);
 
-            var ui = GameObject.FindFirstObjectByType<EC_InventoryUI>();
-            ui?.RefreshAll();
+            {
+                var ui = GameObject.FindFirstObjectByType<EC_InventoryUI>();
+                ui?.RefreshAll();
+                if (purchaseSlotMismatch)
+                {
+                    UnityGameSession.RequestInventoryAsync(0, () =>
+                    {
+                        var ui2 = GameObject.FindFirstObjectByType<EC_InventoryUI>();
+                        ui2?.RefreshAll();
+                    });
+                }
+            }
             UpdateEquipSkins();
         }