Connect Membership to Mailchimp API

Please forgive me, but I’m new at the API thing here. I am trying to set up the site so that when users are changed to a certain Subscription level, they are added to a Mailchimp list.

Here is a screenshot of my Remote Ping that I set up.

I have the Subscription plan set up to talk to the Ping.

I went in and changed a user to the Level that I mentioned above, but nothing seemed to happen on the mailchimp side. I’m assuming that I screwed something up. Can you help me out, please?