<?php
    $sql = "INSERT INTO order_table (o_date, client_id, o_total) VALUES ('$date', $client_id, $order_total);
    if ($con->query($sql)) {
        $order_id = $con->insert_id;

        foreach ($order_lines as $order_line) {
            $sql = "INSERT INTO order_lines (pid, price, color, size, qty, subtotal, order_id) VALUES ($pid, $price,  $color, $size, $qty, $subtotal, $order_id);
            if (!$con->query($sql)) {
                $error[] = $con->error;
            }
        }
    }
?>