OpenCart PHP回调数组问题

我正在尝试编写Netbanx API扩展并访问数组失败。我得到PHP错误的未定义索引的讯问。

数组转储为:

阵列([transaction_status] => success .输出说明[transaction_merchtrefnum] => 476[id] => 271ZH271ZH271Z[transaction_amount] => 4200)

我的Callback函数是:

public function callback() {
    $this->language->load('payment/netbanx_payments');
    $this->load->model('checkout/order');   
    $order_info = $this->model_checkout_order->getOrder($this->session->data['order_id']);
    $this->log->write(print_r($_POST, 1)); //FOR DEBUGGING        
    if(isset($_POST['transaction_merchantRefNum'])){
        $orderId = $_POST['transaction_merchantRefNum'];
        if(in_array($orderId, $_POST)){
                $message = '';
                if (isset($_POST[1])) { 
                    $message .= 'transaction_merchantRefNum: ' . $_POST[1] . "'n";
                }
                if (isset($_POST[3])) {
                    $message .= 'transaction_amount: ' . $_POST[3] . "'n";
                }
                if (isset($_POST[2])) {
                    $message .= 'id: ' . $_POST[2] . "'n";
                }
                if ($_POST[0] == 'success') {
                    $this->model_checkout_order->update($this->request->get['order_id'], $this->config->get('netbanx_payments_order_status_id'), $message, false);
                } else {
                    $this->model_checkout_order->update($this->request->get['order_id'], $this->config->get('config_order_status_id'), $message, false);
                }
                $this->redirect($this->url->link('checkout/success'));
                                unset($myarray);
    }