Mailchimp API 3.0 – PHP and AJAX subscription / unsubscription

function rudr_mailchimp_subscriber_status( $email, $status, $list_id, $api_key, $merge_fields = array('FNAME' => '','LNAME' => '') ){
	$data = array(
		'apikey'        => $api_key,
    	'email_address' => $email,
		'status'        => $status,
		'merge_fields'  => $merge_fields
	);
	$mch_api = curl_init(); // initialize cURL connection
 
	curl_setopt($mch_api, CURLOPT_URL, 'https://' . substr($api_key,strpos($api_key,'-')+1) . '.api.mailchimp.com/3.0/lists/' . $list_id . '/members/' . md5(strtolower($data['email_address'])));
	curl_setopt($mch_api, CURLOPT_HTTPHEADER, array('Content-Type: application/json', 'Authorization: Basic '.base64_encode( 'user:'.$api_key )));
	curl_setopt($mch_api, CURLOPT_USERAGENT, 'PHP-MCAPI/2.0');
	curl_setopt($mch_api, CURLOPT_RETURNTRANSFER, true); // return the API response
	curl_setopt($mch_api, CURLOPT_CUSTOMREQUEST, 'PUT'); // method PUT
	curl_setopt($mch_api, CURLOPT_TIMEOUT, 10);
	curl_setopt($mch_api, CURLOPT_POST, true);
	curl_setopt($mch_api, CURLOPT_SSL_VERIFYPEER, false);
	curl_setopt($mch_api, CURLOPT_POSTFIELDS, json_encode($data) ); // send data in json
 
	$result = curl_exec($mch_api);
	return $result;
}

$email = 'johndoe@rudrastyh.com';
$status = 'subscribed'; // "subscribed" or "unsubscribed" or "cleaned" or "pending"
$list_id = 'YOUR LIST ID HERE'; // where to get it read above
$api_key = 'YOUR MAILCHIMP API KEY HERE'; // where to get it read above
$merge_fields = array('FNAME' => 'Misha','LNAME' => 'Rudrastyh');
 
rudr_mailchimp_subscriber_status($email, $status, $list_id, $api_key, $merge_fields );

<form action="<?php echo site_url() ?>/wp-admin/admin-ajax.php" id="mailchimp">
	<!-- for my website the site_url() function returns https://rudrastyh.com -->
	<input type="text" name="fname" placeholder="First name" />
	<input type="text" name="lname" placeholder="Last name" />
	<input type="email" name="email" placeholder="Email *" required />
 
	<input type="hidden" name="action" value="mailchimpsubscribe" />
	<!-- we need action parameter to receive ajax request in WordPress -->
 
	<button>Subscribe</button>
</form>

jQuery(function($){
	$('#mailchimp').submit(function(){
		var mailchimpform = $(this);
		$.ajax({
			url:mailchimpform.attr('action'),
			type:'POST',
			data:mailchimpform.serialize(),
			success:function(data){
				alert(data);
			}
		});
		return false;
	});
});

function rudr_mch_subscribe(){
	$list_id = 'YOUR LIST ID HERE';
	$api_key = 'YOUR MAILCHIMP API KEY HERE';
	$result = json_decode( rudr_mailchimp_subscriber_status($_POST['email'], 'subscribed', $list_id, $api_key, array('FNAME' => $_POST['fname'],'LNAME' => $_POST['lname']) ) );
	// print_r( $result ); 
	if( $result->status == 400 ){
		foreach( $result->errors as $error ) {
			echo '<p>Error: ' . $error->message . '</p>';
		}
	} elseif( $result->status == 'subscribed' ){
		echo 'Thank you, ' . $result->merge_fields->FNAME . '. You have subscribed successfully';
	}
	// $result['id'] - Subscription ID
	// $result['ip_opt'] - Subscriber IP address
	die;
}
 
add_action('wp_ajax_mailchimpsubscribe','rudr_mch_subscribe');
add_action('wp_ajax_nopriv_mailchimpsubscribe','rudr_mch_subscribe');