not working

the plugin seems to connect to my mailchimp account as it show a green checkmark when the api initial connection is made from your interface…… however when it tries to add a subscriber after the gravity forms is submitted it does not work ……. and the detail in the mail chimp api area shows a red ex and reports a -100 condition?

any idea what might be wrong? is there anything special that needs to be done with the mail chimp list?

https://wordpress.org/plugins/autoresponder/