diff --git a/Backend/ERPCore/Controllers/SalesSlipsController.cs b/Backend/ERPCore/Controllers/SalesSlipsController.cs
new file mode 100644
index 0000000..37601c8
--- /dev/null
+++ b/Backend/ERPCore/Controllers/SalesSlipsController.cs
@@ -0,0 +1,67 @@
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Sales;
+using ERPCore.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ERPCore.Controllers;
+
+[Route("api/v1/sales-slips")]
+public sealed class SalesSlipsController : ApiControllerBase
+{
+    private readonly ISalesSlipService _slips;
+
+    public SalesSlipsController(ISalesSlipService slips) => _slips = slips;
+
+    [HttpGet]
+    [ProducesResponseType(typeof(PagedResponse<SalesSlipSummaryDto>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<PagedResponse<SalesSlipSummaryDto>>> List(
+        [FromQuery] PageQuery query,
+        [FromQuery] SalesSlipStatus? status,
+        [FromQuery] int? customerId,
+        [FromQuery] int? warehouseId,
+        CancellationToken ct)
+        => Ok(await _slips.ListAsync(query, status, customerId, warehouseId, ct));
+
+    [HttpGet("{salesSlipId:int}")]
+    [ProducesResponseType(typeof(SalesSlipDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<SalesSlipDto>> GetById(int salesSlipId, CancellationToken ct)
+    {
+        var result = await _slips.GetAsync(salesSlipId, ct);
+        if (result is null) return NotFound();
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPost]
+    [ProducesResponseType(typeof(SalesSlipDto), StatusCodes.Status201Created)]
+    public async Task<ActionResult<SalesSlipDto>> Create([FromBody] CreateSalesSlipRequest request, CancellationToken ct)
+    {
+        var result = await _slips.CreateAsync(request, ct);
+        SetETag(result.RowVersion);
+        return Created($"/api/v1/sales-slips/{result.Value.SalesSlipId}", result.Value);
+    }
+
+    [HttpPut("{salesSlipId:int}")]
+    [ProducesResponseType(typeof(SalesSlipDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status412PreconditionFailed)]
+    public async Task<ActionResult<SalesSlipDto>> Update(int salesSlipId, [FromBody] UpdateSalesSlipRequest request, CancellationToken ct)
+    {
+        var expected = RequireIfMatch();
+        var result = await _slips.UpdateAsync(salesSlipId, request, expected, ct);
+        SetETag(result.RowVersion);
+        return Ok(result.Value);
+    }
+
+    [HttpPost("{salesSlipId:int}/post")]
+    [ProducesResponseType(typeof(SalesSlipDto), StatusCodes.Status200OK)]
+    public async Task<ActionResult<SalesSlipDto>> Post(int salesSlipId, CancellationToken ct)
+        => Ok(await _slips.PostAsync(salesSlipId, ct));
+
+    [HttpPost("{salesSlipId:int}/cancel")]
+    [ProducesResponseType(typeof(SalesSlipDto), StatusCodes.Status200OK)]
+    public async Task<ActionResult<SalesSlipDto>> Cancel(int salesSlipId, CancellationToken ct)
+        => Ok(await _slips.CancelAsync(salesSlipId, ct));
+}
diff --git a/Backend/ERPCore/Domain/DocumentTypes.cs b/Backend/ERPCore/Domain/DocumentTypes.cs
index b87e7e9..4e1f4ee 100644
--- a/Backend/ERPCore/Domain/DocumentTypes.cs
+++ b/Backend/ERPCore/Domain/DocumentTypes.cs
@@ -18,4 +18,5 @@ public static class DocumentTypes
     /// <summary>Production run (docs/30 FR-MFG-08) — <c>PRD-2026-00001</c>.</summary>
     public const string Production = "PRD";
     public const string SalesInvoice = "SI";
+    public const string SalesSlip = "SSL";
 }
diff --git a/Backend/ERPCore/Domain/Entities/SalesSlip.cs b/Backend/ERPCore/Domain/Entities/SalesSlip.cs
new file mode 100644
index 0000000..46f697a
--- /dev/null
+++ b/Backend/ERPCore/Domain/Entities/SalesSlip.cs
@@ -0,0 +1,36 @@
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Domain.Entities;
+
+public class SalesSlip
+{
+    public int SalesSlipId { get; set; }
+    public string SlipNo { get; set; } = string.Empty;
+    public DateTime SlipDate { get; set; }
+
+    public int CustomerId { get; set; }
+    public Customer? Customer { get; set; }
+
+    public string CustomerSnapshotName { get; set; } = string.Empty;
+    public int WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public int CashierUserId { get; set; }
+    public User? CashierUser { get; set; }
+
+    public SalesSlipStatus Status { get; set; } = SalesSlipStatus.Draft;
+
+    public decimal Subtotal { get; set; }
+    public decimal DiscountTotal { get; set; }
+    public decimal TaxTotal { get; set; }
+    public decimal GrandTotal { get; set; }
+    public decimal PaidAmount { get; set; }
+    public decimal BalanceAmount { get; set; }
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? UpdatedAt { get; set; }
+
+    public uint RowVersion { get; set; }
+
+    public ICollection<SalesSlipLine> Lines { get; set; } = new List<SalesSlipLine>();
+}
diff --git a/Backend/ERPCore/Domain/Entities/SalesSlipLine.cs b/Backend/ERPCore/Domain/Entities/SalesSlipLine.cs
new file mode 100644
index 0000000..c0079e3
--- /dev/null
+++ b/Backend/ERPCore/Domain/Entities/SalesSlipLine.cs
@@ -0,0 +1,35 @@
+namespace ERPCore.Domain.Entities;
+
+public class SalesSlipLine
+{
+    public int SalesSlipLineId { get; set; }
+
+    public int SalesSlipId { get; set; }
+    public SalesSlip? SalesSlip { get; set; }
+
+    public int ItemId { get; set; }
+    public Item? Item { get; set; }
+
+    public string Description { get; set; } = string.Empty;
+
+    public decimal Qty { get; set; }
+    public decimal FreeQty { get; set; }
+    public int UomId { get; set; }
+    public Uom? Uom { get; set; }
+    public int WarehouseId { get; set; }
+    public Warehouse? Warehouse { get; set; }
+
+    public decimal UnitPrice { get; set; }
+    public decimal BaseCost { get; set; }
+    public string PriceSource { get; set; } = string.Empty;
+    public decimal DiscountPct { get; set; }
+    public decimal DiscountAmount { get; set; }
+    public decimal NetUnitPrice { get; set; }
+    public decimal LineTotal { get; set; }
+    public decimal TaxPct { get; set; }
+    public decimal TaxAmount { get; set; }
+    public bool IsFreeIssue { get; set; }
+    public int? ParentLineId { get; set; }
+
+    public uint RowVersion { get; set; }
+}
diff --git a/Backend/ERPCore/Domain/Enums/SalesSlipStatus.cs b/Backend/ERPCore/Domain/Enums/SalesSlipStatus.cs
new file mode 100644
index 0000000..400d11f
--- /dev/null
+++ b/Backend/ERPCore/Domain/Enums/SalesSlipStatus.cs
@@ -0,0 +1,8 @@
+namespace ERPCore.Domain.Enums;
+
+public enum SalesSlipStatus
+{
+    Draft = 1,
+    Posted = 2,
+    Cancelled = 3
+}
diff --git a/Backend/ERPCore/Dtos/Sales/SalesSlipDtos.cs b/Backend/ERPCore/Dtos/Sales/SalesSlipDtos.cs
new file mode 100644
index 0000000..29cf86a
--- /dev/null
+++ b/Backend/ERPCore/Dtos/Sales/SalesSlipDtos.cs
@@ -0,0 +1,55 @@
+using System.ComponentModel.DataAnnotations;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Dtos.Sales;
+
+public sealed record SalesSlipLineDto(
+    int SalesSlipLineId, int ItemId, string Description, decimal Qty, decimal FreeQty, int UomId,
+    int WarehouseId, decimal UnitPrice, decimal BaseCost, string PriceSource, decimal DiscountPct,
+    decimal DiscountAmount, decimal NetUnitPrice, decimal LineTotal, decimal TaxPct, decimal TaxAmount,
+    bool IsFreeIssue, int? ParentLineId);
+
+public sealed record SalesSlipTotalsDto(
+    decimal Subtotal, decimal DiscountTotal, decimal TaxTotal, decimal GrandTotal,
+    decimal PaidAmount, decimal BalanceAmount);
+
+public sealed record SalesSlipDto(
+    int SalesSlipId, string SlipNo, DateTime SlipDate, int CustomerId,
+    string CustomerSnapshotName, int WarehouseId, int CashierUserId, SalesSlipStatus Status,
+    DateTime CreatedAt, DateTime? UpdatedAt, SalesSlipTotalsDto Totals, IReadOnlyList<SalesSlipLineDto> Lines);
+
+public sealed record SalesSlipSummaryDto(
+    int SalesSlipId, string SlipNo, DateTime SlipDate, int CustomerId,
+    string CustomerSnapshotName, int WarehouseId, SalesSlipStatus Status,
+    SalesSlipTotalsDto Totals, DateTime CreatedAt);
+
+public sealed class CreateSalesSlipLineRequest
+{
+    [Required] public int ItemId { get; set; }
+    [Required] public int UomId { get; set; }
+    [Required] public int WarehouseId { get; set; }
+    [Range(0.0001, double.MaxValue)] public decimal Qty { get; set; }
+    [Range(0, double.MaxValue)] public decimal FreeQty { get; set; }
+    [Range(0, double.MaxValue)] public decimal? UnitPrice { get; set; }
+    [Range(0, 100)] public decimal DiscountPct { get; set; }
+    [Range(0, double.MaxValue)] public decimal DiscountAmount { get; set; }
+    [Range(0, 100)] public decimal TaxPct { get; set; }
+    public bool IsFreeIssue { get; set; }
+    public int? ParentLineId { get; set; }
+}
+
+public sealed class CreateSalesSlipRequest
+{
+    [Required] public int CustomerId { get; set; }
+    [Required] public int WarehouseId { get; set; }
+    [Required] public int CashierUserId { get; set; }
+    [Required, MinLength(1)] public List<CreateSalesSlipLineRequest> Lines { get; set; } = new();
+}
+
+public sealed class UpdateSalesSlipRequest
+{
+    [Required] public int CustomerId { get; set; }
+    [Required] public int WarehouseId { get; set; }
+    [Required] public int CashierUserId { get; set; }
+    [Required, MinLength(1)] public List<CreateSalesSlipLineRequest> Lines { get; set; } = new();
+}
diff --git a/Backend/ERPCore/Infra/Persistence/Configurations/SalesSlipConfiguration.cs b/Backend/ERPCore/Infra/Persistence/Configurations/SalesSlipConfiguration.cs
new file mode 100644
index 0000000..deeeed0
--- /dev/null
+++ b/Backend/ERPCore/Infra/Persistence/Configurations/SalesSlipConfiguration.cs
@@ -0,0 +1,95 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace ERPCore.Infra.Persistence.Configurations;
+
+public sealed class SalesSlipConfiguration : IEntityTypeConfiguration<SalesSlip>
+{
+    public void Configure(EntityTypeBuilder<SalesSlip> builder)
+    {
+        builder.ToTable("sales_slips");
+        builder.HasKey(x => x.SalesSlipId);
+
+        builder.Property(x => x.SlipNo).IsRequired().HasMaxLength(50);
+        builder.HasIndex(x => x.SlipNo).IsUnique();
+
+        builder.Property(x => x.SlipDate).IsRequired();
+
+        builder.HasOne(x => x.Customer)
+            .WithMany()
+            .HasForeignKey(x => x.CustomerId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.Property(x => x.CustomerSnapshotName).IsRequired().HasMaxLength(200);
+
+        builder.HasOne(x => x.Warehouse)
+            .WithMany()
+            .HasForeignKey(x => x.WarehouseId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.HasOne(x => x.CashierUser)
+            .WithMany()
+            .HasForeignKey(x => x.CashierUserId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.Property(x => x.Status)
+            .HasConversion<string>().HasMaxLength(20).IsRequired()
+            .HasDefaultValue(SalesSlipStatus.Draft);
+
+        foreach (var p in new[] { nameof(SalesSlip.Subtotal), nameof(SalesSlip.DiscountTotal), nameof(SalesSlip.TaxTotal), nameof(SalesSlip.GrandTotal), nameof(SalesSlip.PaidAmount), nameof(SalesSlip.BalanceAmount) })
+            builder.Property<decimal>(p).HasPrecision(18, 4);
+
+        builder.Property(x => x.CreatedAt).IsRequired();
+        builder.Property(x => x.RowVersion).IsRowVersion();
+
+        builder.HasIndex(x => x.Status);
+        builder.HasIndex(x => x.SlipDate);
+
+        builder.HasMany(x => x.Lines)
+            .WithOne(x => x.SalesSlip)
+            .HasForeignKey(x => x.SalesSlipId)
+            .OnDelete(DeleteBehavior.Cascade);
+    }
+}
+
+public sealed class SalesSlipLineConfiguration : IEntityTypeConfiguration<SalesSlipLine>
+{
+    public void Configure(EntityTypeBuilder<SalesSlipLine> builder)
+    {
+        builder.ToTable("sales_slip_lines");
+        builder.HasKey(x => x.SalesSlipLineId);
+
+        builder.HasOne(x => x.Item)
+            .WithMany()
+            .HasForeignKey(x => x.ItemId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.Property(x => x.Description).IsRequired().HasMaxLength(200);
+
+        builder.Property(x => x.Qty).HasPrecision(18, 4);
+        builder.Property(x => x.FreeQty).HasPrecision(18, 4);
+        builder.Property(x => x.UnitPrice).HasPrecision(18, 4);
+        builder.Property(x => x.BaseCost).HasPrecision(18, 4);
+        builder.Property(x => x.DiscountPct).HasPrecision(9, 4);
+        builder.Property(x => x.DiscountAmount).HasPrecision(18, 4);
+        builder.Property(x => x.NetUnitPrice).HasPrecision(18, 4);
+        builder.Property(x => x.LineTotal).HasPrecision(18, 4);
+        builder.Property(x => x.TaxPct).HasPrecision(9, 4);
+        builder.Property(x => x.TaxAmount).HasPrecision(18, 4);
+
+        builder.HasOne(x => x.Uom)
+            .WithMany()
+            .HasForeignKey(x => x.UomId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.HasOne(x => x.Warehouse)
+            .WithMany()
+            .HasForeignKey(x => x.WarehouseId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.Property(x => x.PriceSource).HasMaxLength(50);
+        builder.Property(x => x.RowVersion).IsRowVersion();
+    }
+}
diff --git a/Backend/ERPCore/Infra/Persistence/ErpDbContext.cs b/Backend/ERPCore/Infra/Persistence/ErpDbContext.cs
index 0719513..ec71934 100644
--- a/Backend/ERPCore/Infra/Persistence/ErpDbContext.cs
+++ b/Backend/ERPCore/Infra/Persistence/ErpDbContext.cs
@@ -86,6 +86,8 @@ public class ErpDbContext : DbContext
     // --- Sales (Phase 1) ---
     public DbSet<SalesInvoice> SalesInvoices => Set<SalesInvoice>();
     public DbSet<SalesInvoiceLine> SalesInvoiceLines => Set<SalesInvoiceLine>();
+    public DbSet<SalesSlip> SalesSlips => Set<SalesSlip>();
+    public DbSet<SalesSlipLine> SalesSlipLines => Set<SalesSlipLine>();
 
     // --- Reference data (docs/10 Part C.7) ---
     public DbSet<ReasonCode> ReasonCodes => Set<ReasonCode>();
diff --git a/Backend/ERPCore/Program.cs b/Backend/ERPCore/Program.cs
index 25e963f..0ace813 100644
--- a/Backend/ERPCore/Program.cs
+++ b/Backend/ERPCore/Program.cs
@@ -91,6 +91,7 @@ builder.Services.AddScoped<IGrnService, GrnService>();
 
 // Sales (Phase 1)
 builder.Services.AddScoped<ISalesInvoiceService, SalesInvoiceService>();
+builder.Services.AddScoped<ISalesSlipService, SalesSlipService>();
 
 // Stock transactions + reference data (docs/11 §5–6)
 builder.Services.AddScoped<IStockMutator, StockMutator>();
diff --git a/Backend/ERPCore/Services/Interfaces/ISalesSlipService.cs b/Backend/ERPCore/Services/Interfaces/ISalesSlipService.cs
new file mode 100644
index 0000000..bd94715
--- /dev/null
+++ b/Backend/ERPCore/Services/Interfaces/ISalesSlipService.cs
@@ -0,0 +1,16 @@
+using ERPCore.Common.Http;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Sales;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Services.Interfaces;
+
+public interface ISalesSlipService
+{
+    Task<PagedResponse<SalesSlipSummaryDto>> ListAsync(PageQuery query, SalesSlipStatus? status, int? customerId, int? warehouseId, CancellationToken ct = default);
+    Task<ETagged<SalesSlipDto>?> GetAsync(int salesSlipId, CancellationToken ct = default);
+    Task<ETagged<SalesSlipDto>> CreateAsync(CreateSalesSlipRequest request, CancellationToken ct = default);
+    Task<ETagged<SalesSlipDto>> UpdateAsync(int salesSlipId, UpdateSalesSlipRequest request, uint expectedRowVersion, CancellationToken ct = default);
+    Task<SalesSlipDto> PostAsync(int salesSlipId, CancellationToken ct = default);
+    Task<SalesSlipDto> CancelAsync(int salesSlipId, CancellationToken ct = default);
+}
diff --git a/Backend/ERPCore/Services/SalesSlipService.cs b/Backend/ERPCore/Services/SalesSlipService.cs
new file mode 100644
index 0000000..3dfb1d8
--- /dev/null
+++ b/Backend/ERPCore/Services/SalesSlipService.cs
@@ -0,0 +1,248 @@
+using ERPCore.Common.Http;
+using ERPCore.Domain;
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using ERPCore.Dtos.Common;
+using ERPCore.Dtos.Sales;
+using ERPCore.Infra.Auth;
+using ERPCore.Infra.UoW;
+using ERPCore.Repositories.Interfaces;
+using ERPCore.Services.Interfaces;
+using ERPCore.Services.Stock;
+using ERPCore.System.Errors;
+using Microsoft.EntityFrameworkCore;
+
+namespace ERPCore.Services;
+
+public sealed class SalesSlipService : ISalesSlipService
+{
+    private readonly IRepository<SalesSlip> _slips;
+    private readonly IRepository<Customer> _customers;
+    private readonly IRepository<Item> _items;
+    private readonly IRepository<Uom> _uoms;
+    private readonly IRepository<Warehouse> _warehouses;
+    private readonly IRepository<User> _users;
+    private readonly IFifoCostingService _fifo;
+    private readonly ICurrentUser _currentUser;
+    private readonly INumberSequenceService _numbers;
+    private readonly IUnitOfWork _uow;
+
+    public SalesSlipService(
+        IRepository<SalesSlip> slips, IRepository<Customer> customers, IRepository<Item> items,
+        IRepository<Uom> uoms, IRepository<Warehouse> warehouses, IRepository<User> users, IFifoCostingService fifo,
+        ICurrentUser currentUser, INumberSequenceService numbers, IUnitOfWork uow)
+    {
+        _slips = slips;
+        _customers = customers;
+        _items = items;
+        _uoms = uoms;
+        _warehouses = warehouses;
+        _users = users;
+        _fifo = fifo;
+        _currentUser = currentUser;
+        _numbers = numbers;
+        _uow = uow;
+    }
+
+    public async Task<PagedResponse<SalesSlipSummaryDto>> ListAsync(PageQuery query, SalesSlipStatus? status, int? customerId, int? warehouseId, CancellationToken ct = default)
+    {
+        IQueryable<SalesSlip> q = _slips.Query().AsNoTracking().Include(x => x.Lines);
+        if (!string.IsNullOrWhiteSpace(query.Q))
+        {
+            var term = query.Q.Trim();
+            q = q.Where(x => EF.Functions.ILike(x.SlipNo, $"%{term}%") || EF.Functions.ILike(x.CustomerSnapshotName, $"%{term}%"));
+        }
+        if (status is not null) q = q.Where(x => x.Status == status);
+        if (customerId is not null) q = q.Where(x => x.CustomerId == customerId);
+        if (warehouseId is not null) q = q.Where(x => x.WarehouseId == warehouseId);
+
+        var total = await q.CountAsync(ct);
+        var rows = await q.OrderByDescending(x => x.SalesSlipId).Skip(query.Skip).Take(query.PageSize).ToListAsync(ct);
+        return PagedResponse<SalesSlipSummaryDto>.Create(rows.Select(MapSummary).ToList(), query.Page, query.PageSize, total);
+    }
+
+    public async Task<ETagged<SalesSlipDto>?> GetAsync(int salesSlipId, CancellationToken ct = default)
+    {
+        var slip = await _slips.Query().AsNoTracking().Include(x => x.Lines)
+            .FirstOrDefaultAsync(x => x.SalesSlipId == salesSlipId, ct);
+        return slip is null ? null : new ETagged<SalesSlipDto>(Map(slip), slip.RowVersion);
+    }
+
+    public async Task<ETagged<SalesSlipDto>> CreateAsync(CreateSalesSlipRequest request, CancellationToken ct = default)
+    {
+        await ValidateReferencesAsync(request.CustomerId, request.WarehouseId, request.CashierUserId, request.Lines, ct);
+
+        var slip = new SalesSlip
+        {
+            SlipNo = await _numbers.NextAsync(DocumentTypes.SalesSlip, ct),
+            SlipDate = DateTime.UtcNow,
+            CustomerId = request.CustomerId,
+            WarehouseId = request.WarehouseId,
+            CashierUserId = request.CashierUserId,
+            Status = SalesSlipStatus.Draft,
+            CreatedAt = DateTime.UtcNow
+        };
+        slip.CustomerSnapshotName = await _customers.Query().Where(x => x.CustomerId == request.CustomerId).Select(x => x.DisplayName ?? x.Name).FirstAsync(ct);
+        slip.Lines = await BuildLinesAsync(request.Lines, ct);
+        Recalculate(slip);
+
+        await _slips.AddAsync(slip, ct);
+        await _uow.SaveChangesAsync(ct);
+        return new ETagged<SalesSlipDto>(Map(slip), slip.RowVersion);
+    }
+
+    public async Task<ETagged<SalesSlipDto>> UpdateAsync(int salesSlipId, UpdateSalesSlipRequest request, uint expectedRowVersion, CancellationToken ct = default)
+    {
+        var slip = await _slips.Query().Include(x => x.Lines).FirstOrDefaultAsync(x => x.SalesSlipId == salesSlipId, ct)
+            ?? throw new NotFoundException($"Sales slip {salesSlipId} was not found.");
+        if (slip.RowVersion != expectedRowVersion)
+            throw new DomainException(ErrorCodes.ConcurrencyConflict, "The sales slip was modified by another request.", 412);
+        if (slip.Status != SalesSlipStatus.Draft)
+            throw new ConflictException($"Sales slip {salesSlipId} is {slip.Status} and cannot be edited.");
+
+        await ValidateReferencesAsync(request.CustomerId, request.WarehouseId, request.CashierUserId, request.Lines, ct);
+        slip.CustomerId = request.CustomerId;
+        slip.WarehouseId = request.WarehouseId;
+        slip.CashierUserId = request.CashierUserId;
+        slip.CustomerSnapshotName = await _customers.Query().Where(x => x.CustomerId == request.CustomerId).Select(x => x.DisplayName ?? x.Name).FirstAsync(ct);
+        slip.Lines.Clear();
+        foreach (var line in await BuildLinesAsync(request.Lines, ct)) slip.Lines.Add(line);
+        Recalculate(slip);
+        slip.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+        return new ETagged<SalesSlipDto>(Map(slip), slip.RowVersion);
+    }
+
+    public async Task<SalesSlipDto> PostAsync(int salesSlipId, CancellationToken ct = default)
+    {
+        var slip = await _slips.Query().Include(x => x.Lines).FirstOrDefaultAsync(x => x.SalesSlipId == salesSlipId, ct)
+            ?? throw new NotFoundException($"Sales slip {salesSlipId} was not found.");
+        if (slip.Status != SalesSlipStatus.Draft)
+            throw new ConflictException($"Sales slip {salesSlipId} is {slip.Status} and cannot be posted.");
+
+        var posted = await _uow.ExecuteInTransactionAsync(async token =>
+        {
+            foreach (var line in slip.Lines)
+            {
+                if (line.Qty <= 0 && line.FreeQty <= 0) continue;
+                var consumed = await _fifo.ConsumeAsync(line.ItemId, line.WarehouseId, null, line.Qty + line.FreeQty, token);
+                var cost = consumed.Count == 0 ? 0m : consumed.Sum(x => x.Qty * x.UnitCost) / consumed.Sum(x => x.Qty);
+                await _fifo.PostLedgerAsync(line.ItemId, line.WarehouseId, null, null, null, _currentUser.AuditUserId,
+                    Direction.Out, line.Qty + line.FreeQty, cost, 0m, nameof(SalesSlip), slip.SalesSlipId, DateTime.UtcNow, token);
+            }
+
+            slip.Status = SalesSlipStatus.Posted;
+            slip.UpdatedAt = DateTime.UtcNow;
+            return slip;
+        }, ct);
+
+        return Map(posted);
+    }
+
+    public async Task<SalesSlipDto> CancelAsync(int salesSlipId, CancellationToken ct = default)
+    {
+        var slip = await _slips.Query().Include(x => x.Lines).FirstOrDefaultAsync(x => x.SalesSlipId == salesSlipId, ct)
+            ?? throw new NotFoundException($"Sales slip {salesSlipId} was not found.");
+        if (slip.Status != SalesSlipStatus.Draft)
+            throw new ConflictException($"Sales slip {salesSlipId} is {slip.Status} and cannot be cancelled.");
+        slip.Status = SalesSlipStatus.Cancelled;
+        slip.UpdatedAt = DateTime.UtcNow;
+        await _uow.SaveChangesAsync(ct);
+        return Map(slip);
+    }
+
+    private async Task ValidateReferencesAsync(int customerId, int warehouseId, int cashierUserId, List<CreateSalesSlipLineRequest> lines, CancellationToken ct)
+    {
+        if (!await _customers.Query().AnyAsync(x => x.CustomerId == customerId, ct))
+            throw new NotFoundException($"Customer {customerId} was not found.");
+        if (!await _warehouses.Query().AnyAsync(x => x.WarehouseId == warehouseId, ct))
+            throw new NotFoundException($"Warehouse {warehouseId} was not found.");
+        if (!await _customers.Query().AnyAsync(x => x.CustomerId == customerId, ct))
+            throw new NotFoundException($"Customer {customerId} was not found.");
+        if (!await _users.Query().AnyAsync(x => x.UserId == cashierUserId, ct))
+            throw new NotFoundException($"User {cashierUserId} was not found.");
+        foreach (var line in lines)
+        {
+            if (!await _items.Query().AnyAsync(x => x.ItemId == line.ItemId, ct))
+                throw new NotFoundException($"Item {line.ItemId} was not found.");
+            if (!await _uoms.Query().AnyAsync(x => x.UomId == line.UomId, ct))
+                throw new NotFoundException($"UOM {line.UomId} was not found.");
+            if (!await _warehouses.Query().AnyAsync(x => x.WarehouseId == line.WarehouseId, ct))
+                throw new NotFoundException($"Warehouse {line.WarehouseId} was not found.");
+        }
+    }
+
+    private async Task<List<SalesSlipLine>> BuildLinesAsync(List<CreateSalesSlipLineRequest> requests, CancellationToken ct)
+    {
+        var lines = new List<SalesSlipLine>();
+        foreach (var r in requests)
+        {
+            var item = await _items.Query().AsNoTracking().FirstAsync(x => x.ItemId == r.ItemId, ct);
+            var priceSource = "SALE_PRICE";
+            decimal unitPrice;
+            if (r.UnitPrice is not null)
+            {
+                unitPrice = r.UnitPrice.Value;
+                priceSource = "MANUAL";
+            }
+            else if (item.SalePrice.HasValue)
+            {
+                unitPrice = item.SalePrice.Value;
+            }
+            else
+            {
+                var valuation = await _fifo.GetValuationAsync(r.ItemId, r.WarehouseId, ct);
+                unitPrice = valuation.TotalQty > 0 ? valuation.TotalValue / valuation.TotalQty : 0m;
+                priceSource = "FIFO_AVG";
+            }
+
+            var gross = r.Qty * unitPrice;
+            var discountAfterPct = gross * (r.DiscountPct / 100m);
+            var discountTotal = discountAfterPct + r.DiscountAmount;
+            var netUnit = r.Qty > 0 ? (gross - discountTotal) / r.Qty : 0m;
+            var lineTotal = gross - discountTotal;
+            var taxAmount = lineTotal * (r.TaxPct / 100m);
+
+            lines.Add(new SalesSlipLine
+            {
+                ItemId = r.ItemId,
+                Description = item.Name,
+                Qty = r.Qty,
+                FreeQty = r.FreeQty,
+                UomId = r.UomId,
+                WarehouseId = r.WarehouseId,
+                UnitPrice = unitPrice,
+                BaseCost = unitPrice,
+                PriceSource = priceSource,
+                DiscountPct = r.DiscountPct,
+                DiscountAmount = discountTotal,
+                NetUnitPrice = netUnit,
+                LineTotal = lineTotal,
+                TaxPct = r.TaxPct,
+                TaxAmount = taxAmount,
+                IsFreeIssue = r.IsFreeIssue,
+                ParentLineId = r.ParentLineId
+            });
+        }
+        return lines;
+    }
+
+    private static void Recalculate(SalesSlip slip)
+    {
+        slip.Subtotal = slip.Lines.Sum(x => x.Qty * x.UnitPrice);
+        slip.DiscountTotal = slip.Lines.Sum(x => x.DiscountAmount);
+        slip.TaxTotal = slip.Lines.Sum(x => x.TaxAmount);
+        slip.GrandTotal = slip.Lines.Sum(x => x.LineTotal) + slip.TaxTotal;
+        slip.PaidAmount = 0m;
+        slip.BalanceAmount = slip.GrandTotal - slip.PaidAmount;
+    }
+
+    private static SalesSlipSummaryDto MapSummary(SalesSlip x) => new(
+        x.SalesSlipId, x.SlipNo, x.SlipDate, x.CustomerId, x.CustomerSnapshotName, x.WarehouseId, x.Status,
+        new SalesSlipTotalsDto(x.Subtotal, x.DiscountTotal, x.TaxTotal, x.GrandTotal, x.PaidAmount, x.BalanceAmount), x.CreatedAt);
+
+    private static SalesSlipDto Map(SalesSlip x) => new(
+        x.SalesSlipId, x.SlipNo, x.SlipDate, x.CustomerId, x.CustomerSnapshotName, x.WarehouseId, x.CashierUserId, x.Status, x.CreatedAt, x.UpdatedAt,
+        new SalesSlipTotalsDto(x.Subtotal, x.DiscountTotal, x.TaxTotal, x.GrandTotal, x.PaidAmount, x.BalanceAmount),
+        x.Lines.Select(l => new SalesSlipLineDto(l.SalesSlipLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.UomId, l.WarehouseId, l.UnitPrice, l.BaseCost, l.PriceSource, l.DiscountPct, l.DiscountAmount, l.NetUnitPrice, l.LineTotal, l.TaxPct, l.TaxAmount, l.IsFreeIssue, l.ParentLineId)).ToList());
+}