Drupal User Registration and Mailchimp API

i have added the mailchimp api to my drupal site but how do i get the user registration form information passed to my mailchimp list. in drupal i have selected user variables to send to mailchimp as merge variables and the mailchimp configuration is set for subscriptions to take place when a user is added or edited but the subscribers do not appear on the mailchimp list.
Thank you in advance for any help you can give.