When you add a domain in the DirectAdmin environment, the software will attempt to fetch and install a free Let's Encrypt SSL certificate in your website. This can take a few minutes and occurs in the background. You will be notified via a control panel message when this is complete.

In the Classic Linux environment, SSL certificates are not automatically fetched, but you can simply go into the SSL certificate menu and manually request a free Let's Encrypt SSL certificate. It will be fetched and automatically installed.