Ping setup for Mailchimp with Membership

Hello!

Just spend a couple of hours trying to get Pings to work with Mailchimp. I have read every post on using Pings with Mailchimp, as well as your video tutorial. It seems everyone is having problems.

Here are my settings:

URL: https://us3.api.mailchimp.com/2.0?

method=listSubscribe
apikey=215XXXXXXXXXXXXXX-us3
id=a34210a4ce
email_address=%useremail%
update_existing=true
send_welcome=false
double_optin=false

Ping method = POST

I did choose to Ping to Subscribe to my list under the Membership Subscription Plan

I am getting a 200-OK message in the Ping History.

Mailchimp's API says the API call was received, method= lists/merge-vars, and Response = n/a.

Mailchimp referred me to WPMUDEV to solve this.

Help!!

Michael