Populating additional content regions in mailchimp_transactional_template

The documentation for this isn't great so I thought I would add some help for anyone struggling to populate multiple regions in a Mailchimp Transactional template.

Code snippet should help:

/**
 * Implements hook_mailchimp_transactional_mail_alter().
 */
function MODULE_mailchimp_transactional_mail_alter(&$mailchimp_transactional_params, $message) {
    switch($mailchimp_transactional_params['message']['id']){
        case 'your_id':
                $some_content = '...';
                $some_other_content = '...';
                $mailchimp_transactional_template_content = [
                    ['name' => 'region_name', 'content' => $some_content],
                    ['name' => 'another_region_name', 'content' => $some_other_content],
                ];
                $mailchimp_transactional_params['message']['mailchimp_transactional_template_content'] = $mailchimp_transactional_template_content;
            }

            break;


    }
}