PHP$_SERVER['；REQUEST_METHOD'；]总是返回带有AJAX帖子的GET

我正在尝试为我的网站设置一个api。我希望有一个单独的页面，根据请求方法执行不同的操作。即GET获取资源，POST创建新资源，PUT更新，DELETE删除。我正在测试$_SERVER['REQUEST_METHOD']变量，看看我应该运行哪个函数，但由于某种原因，无论我的ajax请求如何，它总是显示为get。

第1页

var data = {
            store_id: id,
            reward: reward,
            disclaimer: disclaimer,
            period: period,
            active: active
        }
        //make request to save item
        $.ajax({
                type: "POST",
                url: 'http://' + '<?php echo $base_url; ?>' + 'api/birthday',
                data: data,
                dataType: 'json',
                //headers: {"X-HTTP-Method-Override": "POST"},
                success: function(obj){
                    console.log(obj);
                    $('#save-modal').dialog('open');
                },
                error: function(xhr, textStatus, errorThrown){
                    console.log(arguments);
                    console.log(xhr + '' + textStatus + ' ' + errorThrown);
                }
        });

第2页

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    if( isset($_REQUEST['store_id']) &&
        isset($_REQUEST['reward']) &&
        isset($_REQUEST['disclaimer']) &&
        isset($_REQUEST['period']) &&
        isset($_REQUEST['active']) &&
        is_numeric($_REQUEST['active'])){
            exit(json_encode(update_birthday_reward(filter_var($_REQUEST['store_id'], FILTER_SANITIZE_NUMBER_INT), filter_var($_REQUEST['reward'], FILTER_SANITIZE_STRING), filter_var($_REQUEST['disclaimer'], FILTER_SANITIZE_STRING), filter_var($_REQUEST['period'], FILTER_SANITIZE_STRING), filter_var($_REQUEST['active'], FILTER_SANITIZE_NUMBER_INT))));   
    }else{
        exit(json_encode($_SERVER['REQUEST_METHOD']));
    }
}else if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    if(isset($_REQUEST['store_id'])){
        exit(json_encode(get_birthday_reward($_REQUEST['store_id'])));  
    }else{
        exit(json_encode($_SERVER['REQUEST_METHOD']));
    }
}