Login to your MailChimp account and on the right, click Profile. A new page will load, one of the tabs will say "Extras". Click the Extras tab, a drop down menu will appear, click API from that menu and select, or create an API key.
How to get my MailChimp List ID?
Here's a screenshot of how to get the List ID. Make sure you write it down.
How to get the variables of your ManyChat user?
If you take a look at the JSON at the bottom of this page, you'll notice the first few variables contain values between brackets (). These have to be replaced inside your ManyChat member area. You can get the custom fields in the drop down menu in the dynamic content section where it says Add Variables.
Copy the Code below this line and paste it inside ManyChat's Dynamic Response section
The values between () need to be replaced in your ManyChat section!
Please note: your custom field MUST already exist BEFORE running this flow or you will get an error.