我在我的codeigniter项目中使用了curl来运行API。在本地环境中一切正常。但是在live服务器上出现了问题。
我使用 AJAX 获取数据，然后使用curl调用api。
在我的视图中：

$.ajax({
    type: "POST",
    url: "<?php echo site_url($websitepagename.'/vacancyservice/')?>",
    data: "job_category="+job_category+"&location="+location+"&contract_type="+contract_type+"&search_keyword="+search_keyword,
    success: function(data)
    {
      $("#ajaxBind").html(data);
      // $("html, body").animate({ scrollTop: 0 }, "slow");
    }
  });

在控制器中

function vacancyservice() {     
    $data['response'] = $this->api_call();
    $soap     = simplexml_load_string($data['response']);
    $data['response'] = $soap->children('http://schemas.xmlsoap.org/soap/envelope/')->Body->children()->GetVacancyFeedResponse;
    $this->load->vars($data);
    $this->load->view('ajax_vacancy_list');
}

和控制器中的My Api_call函数

function api_call() {
    $curl = curl_init();

    curl_setopt_array($curl, array(
        CURLOPT_URL => ' API URL ',
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_ENCODING => '',
        CURLOPT_MAXREDIRS => 10,
        CURLOPT_TIMEOUT => 0,
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
        CURLOPT_CUSTOMREQUEST => 'POST',
        CURLOPT_POSTFIELDS =>'<?xml version="1.0" encoding="utf-8"?>
        <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
        <soap:Body>
        <GetVacancyFeed xmlns="http://www1.sniperhire.net/sddf">
        <FeedID>FEEDID</FeedID>
        <Username>USERNAME</Username>
        <Password>PASSWORD</Password>
        </GetVacancyFeed>
        </soap:Body>
        </soap:Envelope>',
        CURLOPT_HTTPHEADER => array(
            'Content-Type: text/xml; charset=utf-8',
            'SOAPAction: SOAP URL'
        ),
    ));

    $response = curl_exec($curl);
    curl_close($curl);
    return $response;
}

此代码在localhost上运行，但在实时服务器上，我得到500 internal server错误和以下错误消息

Message: Call to a member function children() on bool

控制器vacancyservice()中的$data['response'] = $soap->children('http://schemas.xmlsoap.org/soap/envelope/')->Body->children()->GetVacancyFeedResponse;行上指示错误功能

调试结果

经过相当长时间的调试后，我发现在我的api_call()函数中，$response由于某种原因为空，它应该包含XML响应（在localhost上工作正常）