PHP服务器获取内部服务器错误，但直接在URL

Question

我正在尝试从原始PHP（没有框架）制作一个非常简单的API。 当我在浏览器http://localhost/simpleAPI/countries.php上输入时，它会输出我想要的数据。

但是当我使用和ajax调用时，我收到内部服务器错误响应。

<?php
require_once 'Database.php';
header("Content-Type: application/JSON");

$mysqli = Database::getInstance();
$data = [];

    /* Select queries return a resultset */
    if ($result = $mysqli->query("SELECT * FROM Country LIMIT 10")) {

        while ($row = $result->fetch_object()){
            $data[] = $row->Name;
        }
        /* free result set */
        $result->close();
    }

$res = response(200, 'ok', $data);

function response($status, $message , $data){
    header("HTTP/1.1 $status $message"); <-- working Now (after adding $status)
    $res['status'] = $status;
    $res['message'] = $message;
    $res['data'] = $data;

   echo json_encode($res);
}

AJAX

var jqxhr = $.get( "countries.php", function(data) {
                         alert( data);
                    })
                    .done(function() {
                        alert( "second success" );
                    })
                    .fail(function() {
                        alert( "error" );
                    })

错误

jquery.min.js:4 GET http://localhost/simpleAPI/countries.php 500 (Internal Server Error)