diff --git a/SVSim.Database/Services/Inventory/InventoryTransaction.cs b/SVSim.Database/Services/Inventory/InventoryTransaction.cs
index 391d8d2..a6337db 100644
--- a/SVSim.Database/Services/Inventory/InventoryTransaction.cs
+++ b/SVSim.Database/Services/Inventory/InventoryTransaction.cs
@@ -82,7 +82,34 @@ internal sealed class InventoryTransaction : IInventoryTransaction
     }
 
     public Task<SpendResult> TryDebitAsync(UserGoodsType type, long detailId, int num, CancellationToken ct = default)
-        => throw new NotImplementedException();
+    {
+        ThrowIfCommitted();
+        return type switch
+        {
+            UserGoodsType.Crystal => TrySpendAsync(SpendCurrency.Crystal, num, ct),
+            UserGoodsType.Rupy => TrySpendAsync(SpendCurrency.Rupee, num, ct),
+            UserGoodsType.RedEther => TrySpendAsync(SpendCurrency.RedEther, num, ct),
+            UserGoodsType.SpotCardPoint => TrySpendAsync(SpendCurrency.SpotPoint, num, ct),
+            UserGoodsType.Item => Task.FromResult(DebitItem(detailId, num)),
+            _ => throw new NotSupportedException($"Debit not supported for {type}"),
+        };
+    }
+
+    private SpendResult DebitItem(long detailId, int num)
+    {
+        var owned = Viewer.Items.FirstOrDefault(i => i.Item.Id == (int)detailId);
+        if (owned is null)
+            throw new InventoryCatalogException($"Item {detailId} not owned by viewer");
+        if (owned.Count < num)
+            return new SpendResult(SpendOutcome.Insufficient, owned.Count);
+        owned.Count -= num;
+        // Item debit logged as a synthetic SpendOp so CommitAsync can track it.
+        // Sentinel currency (int)-1 is filtered out by CommitAsync's currency-collision loop.
+        _ops.Add(new SpendOp((SpendCurrency)(-1) /* sentinel */, num, owned.Count));
+        // IsCascade: true so this GrantOp is excluded from BuildDeltas output.
+        _ops.Add(new GrantOp(UserGoodsType.Item, detailId, 0, owned.Count, IsCascade: true));
+        return new SpendResult(SpendOutcome.Success, owned.Count);
+    }
 
     public async Task<IReadOnlyList<GrantedReward>> GrantAsync(UserGoodsType type, long detailId, int num, CancellationToken ct = default)
     {
diff --git a/SVSim.UnitTests/Services/Inventory/InventoryDebitTests.cs b/SVSim.UnitTests/Services/Inventory/InventoryDebitTests.cs
new file mode 100644
index 0000000..5412075
--- /dev/null
+++ b/SVSim.UnitTests/Services/Inventory/InventoryDebitTests.cs
@@ -0,0 +1,76 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.Database;
+using SVSim.Database.Enums;
+using SVSim.Database.Models;
+using SVSim.Database.Services;
+using SVSim.Database.Services.Inventory;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Services.Inventory;
+
+public class InventoryDebitTests
+{
+    [Test]
+    public async Task Debit_Crystal_delegates_to_TrySpend()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var ctx = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var v = await ctx.Viewers.FirstAsync(x => x.Id == viewerId);
+        v.Currency.Crystals = 500;
+        await ctx.SaveChangesAsync();
+
+        var inv = scope.ServiceProvider.GetRequiredService<IInventoryService>();
+        await using var tx = await inv.BeginAsync(viewerId);
+        var r = await tx.TryDebitAsync(UserGoodsType.Crystal, 0, 200);
+
+        Assert.That(r.Success, Is.True);
+        Assert.That(r.PostStateTotal, Is.EqualTo(300));
+    }
+
+    [Test]
+    public async Task Debit_Item_decrements_count_and_returns_post_state()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var ctx = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        const int itemId = 32000;
+        var item = new ItemEntry { Id = itemId };
+        ctx.Items.Add(item);
+        var v = await ctx.Viewers.Include(x => x.Items).ThenInclude(i => i.Item).FirstAsync(x => x.Id == viewerId);
+        v.Items.Add(new OwnedItemEntry { Item = item, Count = 10, Viewer = v });
+        await ctx.SaveChangesAsync();
+
+        var inv = scope.ServiceProvider.GetRequiredService<IInventoryService>();
+        await using var tx = await inv.BeginAsync(viewerId);
+        var r = await tx.TryDebitAsync(UserGoodsType.Item, itemId, 3);
+
+        Assert.That(r.Success, Is.True);
+        Assert.That(r.PostStateTotal, Is.EqualTo(7));
+    }
+
+    [Test]
+    public async Task Debit_Item_insufficient_returns_current_count_and_does_not_decrement()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var ctx = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        const int itemId = 32001;
+        var item = new ItemEntry { Id = itemId };
+        ctx.Items.Add(item);
+        var v = await ctx.Viewers.Include(x => x.Items).ThenInclude(i => i.Item).FirstAsync(x => x.Id == viewerId);
+        v.Items.Add(new OwnedItemEntry { Item = item, Count = 2, Viewer = v });
+        await ctx.SaveChangesAsync();
+
+        var inv = scope.ServiceProvider.GetRequiredService<IInventoryService>();
+        await using var tx = await inv.BeginAsync(viewerId);
+        var r = await tx.TryDebitAsync(UserGoodsType.Item, itemId, 5);
+
+        Assert.That(r.Outcome, Is.EqualTo(SpendOutcome.Insufficient));
+        Assert.That(r.PostStateTotal, Is.EqualTo(2));
+    }
+}