Settings - List management
Click under Settings tab on the left menu. Select Mailchimp from the available options.
Enter the API key as shown below and enable the integration via the checkbox. Save your settings.
Once the settings are saved, then we need to establish connectivity with mailchimp. Using the Refresh List option. Clicking that, if everything is setup as above, then your lists in Mailchimp will be retrieved.
Managing your lists is done outside of billmywork. A list created in mailchimp is not retrieved automatically. One must refresh the list and store it when an update is made on mailchimp.
Store the retrieved lists and select a Master list. This helps us determine a default list to store contacts under, in case the customer is not associated with any specific list
Save and you are done.