PHP returning extra whitespace with return statement? - php

Question

My code works, but for some strange reason when I return a string it adds extra space and I think a new line as well.
The code below works fine. However the length of this when fetched with Ajax is 11, the string success has a length of seven so this isn't right and it also doesn't equal to 'success' when comparing.
I've looked through a few other questions but all the solutions they offer don't seem to be working for me. No trailing spaces anywhere as far as I can see. And it's also not coming from any of the files I'm requiring.
<?php
/*
Plugin Name: Quotation Rest API
Plugin URI:
Description: A rest API for sending quotation request through to email using Sendgrid.
Version: 1.0
Author: Niels
Author URI:
*/
add_action( 'rest_api_init', function () {
register_rest_route( 'offerte', '/send',array(
'methods' => 'POST',
'callback' => 'send_mail',
) );
} );
include('MailChimp.php');
use \DrewM\MailChimp\MailChimp;
function send_mail( WP_REST_Request $request) {
$data = $request['data'];
$name = htmlspecialchars($request['name']);
$email = htmlspecialchars($request['email']);
$comment = htmlspecialchars($request['comment']);
$website = htmlspecialchars($request['url']);
$company = htmlspecialchars($request['company']);
$tel = htmlspecialchars($request['tel']);
$mailchimp = htmlspecialchars($request['mailchimp']);
$dataArray = json_decode($data, true);
ob_start();
include('mail.php');
$mailHTML = ob_get_clean();
$success = 'success';
if (!empty($mailchimp)) {
// add email to mailchimp list
$client = new MailChimp('-us14');// get from setttings
$list_id = ' ';// get from setttings
$result = $client->post("lists/$list_id/members", [
'email_address' => $email,
'status' => 'subscribed',
]);
}
$to = " #icloud.com";// get from setttings
$subject = "Offerte van " . $name;// // get from setttings (maybe...)
$message = $mailHTML;
if(wp_mail( $to, $subject, $message)){
return $success;
} else {
// return 'error';
}
}
?>