MailChimp API 3.0 and WordPress HTTP API

get-malichimp-list-data.php

<?php

// Enter MailChimp API key and List Id.
$api_key = 'YOUR API KEY';
$list_id = 'YOUR LIST ID';

$dc = substr($api_key,strpos($api_key,'-')+1); // datacenter, it is the part of your api key - us5, us8 etc
$args = array(
 	'headers' => array(
		'Authorization' => 'Basic ' . base64_encode( 'user:'. $api_key )
	)
);
 
$response = wp_remote_get( 'https://'.$dc.'.api.mailchimp.com/3.0/lists/'.$list_id, $args );
 
$body = json_decode( $response['body'] );
 
if ( $response['response']['code'] == 200 ) {
	echo $body->stats->member_count;
} else {
	echo '<b>' . $response['response']['code'] . $body->title . ':</b> ' . $body->detail;
}