Errors using MailChimp API adding email address to list

I am trying to add email addresses to my mailchimp mailing list but am getting an error saying

Access Denied
You don't have permission to access "http://us9.api.mailchimp.com/3.0/lists/######/members/" on this server.
Reference #18.1e89655f.1546511382.213522b5

I have just created the API key and haven’t done much with MailChimp before. I think the list ID is correct, I just grabbed it from the URL of my actual list in a browser https://us9.admin.mailchimp.com/lists/members/?id=######

<?php

$email = '####@####.##';
$authToken = '#######################-us9';
$email_list = '######';

$postData = array(
    "email_address" => "$email", 
    "status" => "subscribed",
    "merge_fields" => array(
    "NAME"=> "",
    "PHONE"=> "")
);

$ch = curl_init('https://us9.api.mailchimp.com/3.0/lists/'.$email_list.'/members/');

curl_setopt_array($ch, array(
    CURLOPT_POST => TRUE,
    CURLOPT_RETURNTRANSFER => TRUE,
    CURLOPT_HTTPHEADER => array(
        'Authorization: apikey '.$authToken,
        'Content-Type: application/json'
    ),
    CURLOPT_POSTFIELDS => json_encode($postData)
));

$response = curl_exec($ch);

var_dump($response);

?>

Answer

The API list ID is not the same as the browser one. (Don’t ask me why). To find out the API list ID, use the API Playground. https://developer.mailchimp.com/