Super shows a 404 error mainly because of three factors:
The page is not a subpage in Notion
Super only publishes pages that are added as subpages of your main (parent) Notion page. If a page exists outside this structure or as a standalone/orphan page, Super won’t recognize it as part of your site and will return a 404 error.The page is not published
If a page is not published or shared properly in Notion, Super cannot access it, which also results in a 404 error on the live site.The page has been deleted or moved to Trash in Notion
If a page has been deleted or moved to Notion’s Trash, it is no longer accessible. Since Super can’t retrieve deleted pages, the URL will show a 404 error.
To resolve this:
Make sure each page is set up as a subpage in Notion.
Publish your Notion pages by clicking the Share button in the upper-right corner, then selecting Publish.
Go to Super and trigger the refresh button in your dashboard preview.
You can check this FAQ's - I'm seeing error 404 on my page for a video guide. Pages that exist outside your connected Notion site or are no longer accessible will consistently show a 404 error. Requiring pages to be properly structured as subpages helps maintain security and content integrity, ensuring that only intended pages are publicly accessible.
In short:
For a page to work in Super, it must be a subpage, published, and not deleted in Notion so Super can detect it and display it correctly.