php如何接入paypal支付

<form action="https://www.paypal.com/cgi-bin/webscr" method="post" name="paypal">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="business" value="paypal收款账号">
<input type="hidden" name="item_name" value="商品名称-PCB Online Payment">
<input type="hidden" name="item_number" value="可以写入订单ID（备选项）">
<input type="hidden" name="cancel_return" value="取消支付返回url">    
<input type="hidden" name="notify_url" value="支付完成返回url">   
<input type="hidden" name="return" value="支付完成返回url">  
<!-- 货币种类，USD为美元 -->
<input type="hidden" name="currency_code" value="USD">
<!-- 支付金额 -->
<input type="hidden" name="amount" value="8.88">
<input type="submit" value="立即支付" class="sbtn4" />
</form>

/**
*处理返回信息的方法
*/
public function notify(){
        if ($this->user_id == false){
            $this->redirect('user/login');
        }
        $result = $_POST;
        $order_id = $result['item_number'];
        if ($order_id){
            $order = D('order')->find($order_id);
            $this->assign('order_num',$order['order_num']);
            //1、先更新订单状态
            if (($order['pay_status'] == 0) && ($result['payment_status'] == 'Completed') ){// 支付成功
                $this->update_order($result);
            }
            //2、才能添加支付记录
            if ($order['pay_status'] == 0){
                $this->add_payment_logs($result);
            }
        }
        $this->assign('order_id',$order_id);
        $this->assign('payment_status',$result['payment_status']);
        $this->assign('payment_gross',$result['payment_gross']);
        $this->assign('seo_title','notify');
        $this->display();
    }