Assuming you already have an MailerLite account. To successfully configure the Autoresponder you’ll be requiring just one parameter, which is API Key.

Step 1 : Login to your MailerLite account and click on your user name, in the drop down list go to Integrations as shown below :

Step 2 : A new page will open. You need to click on USE button (which is in front of Developer API)  as shown below :

Step 3 : At the top left, you will see the API key as shown below :

Copy this key and paste in configuration box in AR settings area. That’s it !