如何在Mailchimp中仅获取成员字段名称（电子邮件地址，名字，姓氏）

I am trying to get all the fields name against list in mailchimp fields like email address , firstname and last name etc. I am new in mailchimp i am testing with postman:

My controller code:

    public function getFields()
{
    $list = 'ba6de7f809';
    $ch = curl_init(REQUEST_URL.$list.'/members/?fields=members.email_address','members.first_name','members.last_name');

    curl_setopt($ch, CURLOPT_USERPWD, 'user:' . 'xyz-us17');
    curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_TIMEOUT, 10);
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'GET');
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

    $result = curl_exec($ch);
    $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    $error = curl_error ( $ch );
    curl_close($ch);
}

and my api route:

   Route::get('getFields','ApiController@getFields');

I know there is some mistakes in my controller code i am declaring the list id in variable is it correct way to declare? and when i hit url in postman it says and i am using laravel 5.5.

 Use of undefined constant REQUEST_URL - assumed 'REQUEST_URL' (this will throw an Error in a future version of PHP)

Can anyone please guide how to fetch fields name from this code: Any help would be highly appreciated!

in you controller code

 $ch = curl_init(REQUEST_URL.$list.'/members/?fields=members.email_address','members.first_name','members.last_name');

The REQUEST_URL you have used is not defined anywhere.

somewhere in you class you have to define the constant

const REQUEST_URL = 'https://usX.api.mailchimp.com/3.0'

I presume you could get this url from you mailchimp account

Additionally to get the user fields, rather than using /members/ endpoint you should use the search_members endpoint