Integrating Leadformly with Mailchimp is very easy and quick, simply use the following steps:
Go to your account settings in Mailchimp and find your API key
Go to the builder page of your form in the Leadformly app and scroll down to the 'Call To Action' section
Switch the toggle 'Send lead to email services' and select 'Mailchimp'

Enter the Mailchimp API key and select the appropriate Mailchimp email list
Map the questions with the Mailchimp fields
Save and customise the form, embed it on your website
Remember to test your form and generate a lead. The lead should automatically get added to your selected Mailchimp list.
You may need to double check your double opt-in settings in Mailchimp and switch them on/off as required.