How to enable the newsletter subscription option in the chat window?
Navigate to Settings > Websites > Website-name > Live Chat Window > Fields.
Hover over the option Newsletter Subscription.
A dialog box will appear, enter the text you would like to display to your website visitors in the chat window. Then, choose a mailing list from the drop down and click save.
Now, the visitors who access the chat widget on your website will be able to view the Newsletter subscription option in the pre-chat survey window.