How to Get MailChimp List ID
To use Contact Form 7 MailChimp Extension, you need to obtain your MailChimp API key, follow these steps to find it.
Users with Manager permissions can generate and view their own API keys. Users with Admin permissions can also see API keys for other account users. Below, you’ll learn how to grab an existing API key or generate a new one.
Login to your MailChimp account here: https://admin.mailchimp.com/lists/
Once you click the link highlighted (yellow) above you will be presented with the MailChimp List ID at the bottom of the Settings page
Input your MailChimp List ID in the appropriate field inside Contact Form 7 MailChimp Extension
I hope this was a useful explanation of how to get a MailChimp List ID Key to use with Contact Form 7 MailChimp Extension.