<?php

require_once 'vendor/autoload.php';
use MailerLite\Campaigns;
// $campaigns = new Campaigns('934f72f4e4cc944c54f3f1d7942f979a');
// $all = $campaigns->getAll();
// from the form
$name = trim(strip_tags($_POST['name']));
$email = trim(strip_tags($_POST['email']));
$bus_name = htmlentities($_POST['bus_name']);
if (empty($name) || empty($email) || empty($bus_name)) {
    $success = false;
    return $success;
}
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $success = false;
    return $success;
}
$ML_Subscribers = new MailerLite\Subscribers('934f72f4e4cc944c54f3f1d7942f979a');
$subscriber = array('name' => $name, 'email' => $email, 'fields' => array(array('name' => 'bus_name', 'value' => $bus_name)));
if ($subscriber = $ML_Subscribers->setId('3234849')->add($subscriber)) {
    $success = true;
} else {
    $success = false;
}
// Response to ajax
if ($success) {
    echo "success";
} else {
    echo "invalid";
}
<?php

require_once 'vendor/autoload.php';
use MailerLite\Campaigns;
// $campaigns = new Campaigns('934f72f4e4cc944c54f3f1d7942f979a');
// $all = $campaigns->getAll();
// from the form
$email = trim(strip_tags($_POST['email']));
if (empty($email)) {
    $success = false;
    return $success;
}
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $success = false;
    return $success;
}
$ML_Subscribers = new MailerLite\Subscribers('934f72f4e4cc944c54f3f1d7942f979a');
$subscriber = array('email' => $email);
if ($subscriber = $ML_Subscribers->setId('3243741')->add($subscriber)) {
    $success = true;
} else {
    $success = false;
}
// Response to ajax
if ($success) {
    echo "success";
} else {
    echo "invalid";
}