Answered Add subscriber to MailChimp through posthook

<?php
$checked = $hook->getValue('newsletter');
$fname = $hook->getValue('fname');
$lname = $hook->getValue('lname');
$email = $hook->getValue('email');
$listId = $hook->getValue('listid');
$apiKey = "TheAPIkeyinMailchimp";
$server = "us2";

if ($checked == "Yes") {
    $memberId = md5(strtolower($email));
    print $url = 'https://' . $server . '.api.mailchimp.com/3.0/lists/' . $listId . '/members/' . $memberId;

    $data = array(
        'email_address'=>$email,
        'status' => 'pending',
        'merge_fields'  => [
            'FNAME'     => $fname,
            'LNAME'     => $lname            
        ]
        );
    $jsonString = json_encode($data);

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

}