When you are ready to launch a Domain in Composer you can switch it from “Production” mode to “Live” mode in order to accept the DNS changes on the domain. You should only set and confirm your site go live when, or just before, your DNS settings have been updated to launch your site. This article does not apply to Page Manager to Composer Redesigns
To set your site "Live", find the Domain Settings section for the appropriate Domain in Composer. It is located by hovering over the Domain and clicking the 3 dot overflow menu and selecting “Settings” .For each Domain in Composer, there are Domain Settings accessible by hovering over the Domain and clicking the 3 dot overflow menu.
Under the “General” tab, you’ll see the Domain’s Primary URL and a “Domain is live” checkbox in the Host Names section. Click the “Domain is live” checkbox. One the next screen, enter the Primary URL as validation that you are sure you’re ready to go live and click "Confirm". Click "Apply" in the domain settings modal to apply the update.
This box should ONLY be checked when, or just before, your DNS settings have been updated to launch the site. Checking the box may create broken links in some areas of your site until the DNS updates are revolving properly.