// Add Shortcode
function mailpoet_bulk_subscribe_func()
{

    ob_start(); ?>

    <form action="?submit=true" method="POST">
        <input name="email" type="text" required placeholder="Email address">
        <input name="first_name" type="text" placeholder="First name">
        <input name="last_name" type="text" placeholder="Last name">
        <input type="checkbox" name="lists[]" value="1"/>List 1<br/>
        <input type="checkbox" name="lists[]" value="2"/>List 2<br/>
        <input value="Subscribe!" type="submit">
    </form>

    <?php

    $content = ob_get_contents();

    ob_end_clean();

    $slide = (isset($_GET["submit"]) && trim($_GET["submit"]) == 'true') ? trim($_GET["submit"]) : '';


    if ("true" === $slide) {
        $subscriber_data = array(
            'email' => sanitize_text_field($_POST['email']),
            'first_name' => sanitize_text_field($_POST['first_name']),
            'last_name' => sanitize_text_field($_POST['first_name'])
        );

        $options = array(
            'send_confirmation_email' => true,// default: true
            'schedule_welcome_email' => false // default: true
        );

        $lists = array_map('intval', $_POST['lists']);

        try {
            $subscriber = \MailPoet\API\API::MP('v1')->addSubscriber($subscriber_data, $lists, $options);
        } catch (Exception $exception) {
            return $exception->getMessage();
        }
    }



    return $content;

}
add_shortcode('mailpoet_bulk_subscribe', 'mailpoet_bulk_subscribe_func');