diff --git a/Frontend/erp-system/lib/format-uom.ts b/Frontend/erp-system/lib/format-uom.ts
new file mode 100644
index 0000000..fbcea27
--- /dev/null
+++ b/Frontend/erp-system/lib/format-uom.ts
@@ -0,0 +1,41 @@
+const UOM_LABELS: Record<string, string> = {
+  BAG: "Bag",
+  BOX: "Box",
+  BTL: "Bottle",
+  CAN: "Can",
+  CM: "Centimeter",
+  CTN: "Carton",
+  DOZ: "Dozen",
+  EA: "Each",
+  G: "Gram",
+  KG: "Kilogram",
+  L: "Litre",
+  M: "Meter",
+  ML: "Millilitre",
+  MM: "Millimeter",
+  PACK: "Pack",
+  PCS: "Pieces",
+  PK: "Pack",
+  PKT: "Packet",
+  ROLL: "Roll",
+  SET: "Set",
+}
+
+export function formatUomName(name: string | null | undefined): string {
+  const normalized = name?.trim()
+  if (!normalized) return ""
+
+  const mapped = UOM_LABELS[normalized.toUpperCase()]
+  if (mapped) return mapped
+
+  if (/^[A-Z0-9/_-]+$/.test(normalized)) {
+    return normalized.charAt(0) + normalized.slice(1).toLowerCase()
+  }
+
+  return normalized
+}
+
+export function findUomLabel(uoms: Array<{ uomId: number; name: string }>, uomId: number): string {
+  const name = uoms.find((uom) => uom.uomId === uomId)?.name
+  return name ? formatUomName(name) : `#${uomId}`
+}
diff --git a/Frontend/erp-system/lib/sales-validation.ts b/Frontend/erp-system/lib/sales-validation.ts
new file mode 100644
index 0000000..c5b2eda
--- /dev/null
+++ b/Frontend/erp-system/lib/sales-validation.ts
@@ -0,0 +1,101 @@
+type SalesEditableLine = {
+  itemId: number
+  uomId: number
+  warehouseId: number
+  qty: number
+  freeQty: number
+  unitPrice?: number | null
+  discountPct?: number
+  taxPct?: number
+}
+
+type SalesDocumentValidationInput = {
+  customerId: number | null
+  warehouseId: number | null
+  cashierUserId?: number | null
+  requireCashierUser?: boolean
+  lines: SalesEditableLine[]
+  lineLabel?: string
+}
+
+type BundleEditableLine = {
+  itemId: number
+  uomId: number
+  qty: number
+  unitPrice: number
+}
+
+type BundleValidationInput = {
+  customerId: number | null
+  warehouseId: number | null
+  cashierUserId: number | null
+  templateId: number | null
+  bundleName: string
+  bundlePrice: number
+  lines: BundleEditableLine[]
+}
+
+function invalidNumber(value: number | null | undefined) {
+  return value === null || value === undefined || !Number.isFinite(value)
+}
+
+export function validateSalesDocument(input: SalesDocumentValidationInput): string | null {
+  const {
+    customerId,
+    warehouseId,
+    cashierUserId,
+    requireCashierUser = false,
+    lines,
+    lineLabel = "line",
+  } = input
+
+  if (!customerId) return "Select a customer."
+  if (!warehouseId) return "Select a warehouse."
+  if (requireCashierUser && !cashierUserId) return "Select a cashier."
+  if (lines.length === 0) return `Add at least one ${lineLabel}.`
+
+  for (const [index, line] of lines.entries()) {
+    const row = index + 1
+    if (!line.itemId) return `Select an item for ${lineLabel} ${row}.`
+    if (!line.uomId) return `Select a valid UOM for ${lineLabel} ${row}.`
+    if (!line.warehouseId) return `Select a warehouse for ${lineLabel} ${row}.`
+    if (warehouseId && line.warehouseId !== warehouseId) {
+      return `${lineLabel[0]?.toUpperCase() ?? "L"}${lineLabel.slice(1)} ${row} warehouse must match the selected header warehouse.`
+    }
+    if (invalidNumber(line.qty) || line.qty <= 0) return `Enter a quantity greater than zero for ${lineLabel} ${row}.`
+    if (invalidNumber(line.freeQty) || line.freeQty < 0) return `Enter a valid free quantity for ${lineLabel} ${row}.`
+    if (line.unitPrice !== null && line.unitPrice !== undefined && (invalidNumber(line.unitPrice) || line.unitPrice < 0)) {
+      return `Enter a valid unit price for ${lineLabel} ${row}.`
+    }
+    if (line.discountPct !== undefined && (invalidNumber(line.discountPct) || line.discountPct < 0 || line.discountPct > 100)) {
+      return `Enter a discount percentage between 0 and 100 for ${lineLabel} ${row}.`
+    }
+    if (line.taxPct !== undefined && (invalidNumber(line.taxPct) || line.taxPct < 0 || line.taxPct > 100)) {
+      return `Enter a tax percentage between 0 and 100 for ${lineLabel} ${row}.`
+    }
+  }
+
+  return null
+}
+
+export function validateBundleSale(input: BundleValidationInput): string | null {
+  const { customerId, warehouseId, cashierUserId, templateId, bundleName, bundlePrice, lines } = input
+
+  if (!customerId) return "Select a customer."
+  if (!warehouseId) return "Select a warehouse."
+  if (!cashierUserId) return "Select a cashier."
+  if (!templateId) return "Select a bundle template."
+  if (!bundleName.trim()) return "Enter a bundle name."
+  if (invalidNumber(bundlePrice) || bundlePrice < 0) return "Enter a valid bundle price."
+  if (lines.length === 0) return "Add at least one bundle component line."
+
+  for (const [index, line] of lines.entries()) {
+    const row = index + 1
+    if (!line.itemId) return `Select an item for component line ${row}.`
+    if (!line.uomId) return `Select a valid UOM for component line ${row}.`
+    if (invalidNumber(line.qty) || line.qty <= 0) return `Enter a quantity greater than zero for component line ${row}.`
+    if (invalidNumber(line.unitPrice) || line.unitPrice < 0) return `Enter a valid unit price for component line ${row}.`
+  }
+
+  return null
+}