all, I have tried following the successful method posted

Hi all, I have tried following the successful method posted in this other thread:
https://premium.wpmudev.org/forums/topic/membership-mailchimp-auto-subscribe-ping

When I tested a week ago, it worked (yay!). When I went live with my new subscrption today... nothing. Pings are working and in Ping History it shows them all as "OK" but there is no activity on Mailchimp.

I tried manually pinging as described above:
http://us7.api.mailchimp.com/1.3/&method=listSubscribe&apikey=18900370f23efc8c9c08dfd0fc256475-us7&id=dc351d4f0e&email_address=test@rollerderbyathletics.com&send_welcome=false&update_existing=true&double_optin=false&

And I received a 404 page.

What do you think I'm doing wrong?
Here is my ping data:

Ping url: http://us7.api.mailchimp.com/1.3/
Ping Data:
method=listSubscribe
apikey=18900370f23efc8c9c08dfd0fc256475-us7
id=dc351d4f0e
email_address=%useremail%
send_welcome=false
update_existing=true
double_optin=false