404 errors indicate that the webpage you are trying to reach either can't be found or has been deleted. Don't worry, there are a few steps that you can take to restore the webpage (as long as the page has not been deleted).
Possible reasons why you may see a 404 error:
The page you were on in the B12 Editor is hidden and you selected to Preview or Publish (you can learn how to show a hidden page here).
The URL has changed (this can happen if a page has been renamed)
The URL no longer exists
The URL was mistyped
Here some fixes that you can implement depending on the reason outlined above:
If you need any help, please reach out to our Customer Support team!