composer require drewm/mailchimp-api

- My-Project
  - application
  - system
  - vendor
    - composer
    - drewm
      - mailchimp-api
        - src
          Batch.php
          MailChimp.php
          Webhook.php
      autoload.php

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

require("vendor/autoload.php")

use DrewMMailChimpMailChimp;

$MailChimp = new MailChimp('abc123abc123abc123abc123abc123-us1');


class Newsletter extends CI_Controller {

public function __construct()
{
    parent::__construct();
    // Your own constructor code
    // $this->load->model(array('frontend/m_home'));
}

public function mailchimp()
{
    $list_id = 'fe0c4f267c';

    $result = $MailChimp->post("lists/$list_id/members", [
                    'email_address' => 'davy@example.com',
                    'status'        => 'subscribed',
                ]);

    if ($MailChimp->success()) {
        print_r($result);
    } else {
        echo $MailChimp->getLastError();
    }
} }

<div class="content">
            <?php echo form_open('newsletter'); ?>
            <h4>Subscribe to Our Newsletter</h4>
            <input name="name" class="newaletter-email" type="text" placeholder="Your name"></input>
            <input class="newaletter-email" type="email" placeholder="Your Email"></input>
            <button name="submit" type="submit" class="leka-button"> Subscribe </button>
            <?php echo form_close(); ?>
        </div>