Fatal error: Uncaught PDOException: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'order_id' in 'field list'

Question

$statement = $conn->query("SELECT LAST_INSERT_ID()");
$order_id = $statement->fetchColumn();
for($count=0; $count<$_POST["total_item"]; $count++)
{
$sub_total = $sub_total + floatval(trim($_POST["order_item_actual_amount"][$count]));
$discount = $discount + floatval(trim($_POST["discount_amount"][$count]));
$total_after_discount = $total_after_discount + floatval(trim($_POST["order_item_final_amount"][$count]));
$statement = $conn->prepare("
INSERT INTO tbl_medlab_item
(order_id,item_type, item_name, order_item_quantity, order_item_price, order_item_actual_amount, discount, discount_amount, order_item_final_amount)
VALUES (:order_id, :item_type, :item_name, :order_item_quantity, :order_item_price, :order_item_actual_amount, :discount, :discount_amount, :order_item_final_amount)
");
//order_id IS PRESENT IN BOTH TABLE (tbl_medlab and tbl_medlab_item)
$statement->execute(
array(
':order_id' => $order_id,
':item_type' => trim($_POST["item_type"][$count]),
':item_name' => trim($_POST["item_name"][$count]),
':order_item_quantity' => trim($_POST["order_item_quantity"][$count]),
':order_item_price' => trim($_POST["order_item_price"][$count]),
':order_item_actual_amount' => trim($_POST["order_item_actual_amount"][$count]),
':discount' => trim($_POST["discount"][$count]),
':discount_amount' => trim($_POST["discount_amount"][$count]),
//ERROR PART START HERE
':order_item_final_amount' => trim($_POST["order_item_final_amount"][$count])
//ERROR PART END's HERE
)
);
}