Pings to Mailchimp

Hi. I have a question about the the Membership Pings. I would like to each user to be added to a membership mailing list that I'm using via Mailchimp. I followed each step in the Membership Plugin's Manual but can't get it to work.

I have it setup to ping once they sign up via one of the Subscription Plans. There seems to be some action because the Ping History is showing a list of pings. However, nothing is showing up in the Status column and nothing is showing up in my Mailchimp account.

Do you see anything wrong with my code below? Thanks.

Ping URL: http://us1.api.mailchimp.com/1.3/?

method=listSubscribe
apikey= ***
id= ****
email_address=%useremail%
double_optin=false
update_existing=true
send_welcome=false