fix: FG Item incorrect qty in the work order (#39200)

diff --git a/erpnext/manufacturing/doctype/production_plan/production_plan.py b/erpnext/manufacturing/doctype/production_plan/production_plan.py
index 2bfd4be..f64af50 100644
--- a/erpnext/manufacturing/doctype/production_plan/production_plan.py
+++ b/erpnext/manufacturing/doctype/production_plan/production_plan.py
@@ -646,6 +646,10 @@
 				"project": self.project,
 			}
 
+			key = (d.item_code, d.sales_order, d.warehouse)
+			if not d.sales_order:
+				key = (d.name, d.item_code, d.warehouse)
+
 			if not item_details["project"] and d.sales_order:
 				item_details["project"] = frappe.get_cached_value("Sales Order", d.sales_order, "project")
 
@@ -654,12 +658,9 @@
 				item_dict[(d.item_code, d.material_request_item, d.warehouse)] = item_details
 			else:
 				item_details.update(
-					{
-						"qty": flt(item_dict.get((d.item_code, d.sales_order, d.warehouse), {}).get("qty"))
-						+ (flt(d.planned_qty) - flt(d.ordered_qty))
-					}
+					{"qty": flt(item_dict.get(key, {}).get("qty")) + (flt(d.planned_qty) - flt(d.ordered_qty))}
 				)
-				item_dict[(d.item_code, d.sales_order, d.warehouse)] = item_details
+				item_dict[key] = item_details
 
 		return item_dict
 
diff --git a/erpnext/manufacturing/doctype/production_plan/test_production_plan.py b/erpnext/manufacturing/doctype/production_plan/test_production_plan.py
index f6dfaa5..fedeb7a 100644
--- a/erpnext/manufacturing/doctype/production_plan/test_production_plan.py
+++ b/erpnext/manufacturing/doctype/production_plan/test_production_plan.py
@@ -672,7 +672,7 @@
 			items_data = pln.get_production_items()
 
 			# Update qty
-			items_data[(item, None, None)]["qty"] = qty
+			items_data[(pln.po_items[0].name, item, None)]["qty"] = qty
 
 			# Create and Submit Work Order for each item in items_data
 			for key, item in items_data.items():
@@ -1522,6 +1522,45 @@
 		for d in mr_items:
 			self.assertEqual(d.get("quantity"), 1000.0)
 
+	def test_fg_item_quantity(self):
+		from erpnext.stock.doctype.warehouse.test_warehouse import create_warehouse
+		from erpnext.stock.utils import get_or_make_bin
+
+		fg_item = make_item(properties={"is_stock_item": 1}).name
+		rm_item = make_item(properties={"is_stock_item": 1}).name
+
+		make_bom(item=fg_item, raw_materials=[rm_item], source_warehouse="_Test Warehouse - _TC")
+
+		pln = create_production_plan(item_code=fg_item, planned_qty=10, do_not_submit=1)
+
+		pln.append(
+			"po_items",
+			{
+				"item_code": rm_item,
+				"planned_qty": 20,
+				"bom_no": pln.po_items[0].bom_no,
+				"warehouse": pln.po_items[0].warehouse,
+				"planned_start_date": add_to_date(nowdate(), days=1),
+			},
+		)
+		pln.submit()
+		wo_qty = {}
+
+		for row in pln.po_items:
+			wo_qty[row.name] = row.planned_qty
+
+		pln.make_work_order()
+
+		work_orders = frappe.get_all(
+			"Work Order",
+			fields=["qty", "production_plan_item as name"],
+			filters={"production_plan": pln.name},
+		)
+		self.assertEqual(len(work_orders), 2)
+
+		for row in work_orders:
+			self.assertEqual(row.qty, wo_qty[row.name])
+
 
 def create_production_plan(**args):
 	"""