Newly generated Atlas pages run on an app embed called Atlas Page Builder. This embed is turned off by default, so the first time you publish a new page you'll enable it once in your theme. After that, it stays on for all your future pages.
Until the embed is enabled, the Publish button in the Atlas editor stays inactive and you'll see a message titled "Enable Atlas in your theme to publish."
In this article:
The fastest way: Activate app embed
When you go to publish a new page, the editor shows a box titled "Enable Atlas in your theme to publish."
In that box, click the Activate app embed button
This opens your theme editor with the App embeds panel ready
Find Atlas Page Builder and toggle it on
Click Save in the top right of the theme editor
Return to the Atlas editor
Atlas re-checks automatically, so once you've saved, the Publish button becomes active.
Enabling it manually
If the Activate app embed button doesn't open the theme editor for you, you can turn the embed on manually:
From your Shopify admin, go to Online Store > Themes
Click Customize on the theme you're publishing to
Click the App embeds icon in the left sidebar (the puzzle-piece icon)
Locate Atlas Page Builder in the list
Toggle it on
Click Save
TIP: The Atlas Page Builder embed has no settings to configure. You only need to toggle it on and save.
After you enable it
Once the embed is on and saved, head back to the Atlas editor. The Publish button will be active, and you can publish your page as normal. You won't need to repeat this step for future pages on the same theme, the embed stays enabled.
NOTE: Make sure you enable the embed on the theme you're actually publishing to. The Atlas editor shows which theme that is under "Publishing to" in the publish panel.
Why this is needed
The app embed is what powers Atlas pages inside your theme. Enabling it lets your generated pages display correctly and gives you added flexibility, like deleting sections in the Shopify Customizer and adding Atlas sections to other templates. For the bigger picture on this change, see What's new with Atlas: pages now run on an app embed.