คำสั่ง INSERT ทำงานแต่ คำสั่ง UPDATE ไม่ทำงานค๊ะ ทำอย่างไรดีค๊ะ

        $sql = mysql_query("INSERT INTO `payments` (txnid, payment_amount, payment_status,percent_discount) VALUES (
                '".$data['txn_id']."' ,
                '".$data['payment_amount']."' ,
                '".$data['payment_status']."' ,
                '".$data['percent_discount']."'
                )", $link);


             $sql = "UPDATE  option SET  	quantity = '0' , 
                                                closed = '1' , 
                                                end_time = 'now'
                                          WHERE id = '15' ";