PHP cURL function to add subscriber to MailChimp API 3.0

mailchimp.php

<?php
$data = [
  'email'     => $email,
  'status'    => 'subscribed',
  'firstname' => $fname,
  'lastname'  => $lname
];

function syncMailchimp($data) {
  $apiKey = 'XXX';
  $listId = 'XXX';

  $memberId = md5(strtolower($data['email']));
  $dataCenter = substr($apiKey,strpos($apiKey,'-')+1);
  $url = 'https://' . $dataCenter . '.api.mailchimp.com/3.0/lists/' . $listId . '/members/' . $memberId;

  $json = json_encode([
      'email_address' => $data['email'],
      'status'        => $data['status'], // "subscribed","unsubscribed","cleaned","pending"
      'merge_fields'  => [
          'FNAME'     => $data['firstname'],
          'LNAME'     => $data['lastname']
      ]
  ]);

  $ch = curl_init($url);

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

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

  return $httpCode;
}

syncMailchimp($data);

?>