Setup custom 404 error page
Create a new "Code file" in your # folder
Navigate to your published folders root folder.
Create or open the # folder.
Click new and choose "Code File"
Name the file "404.hash"
Enter any desired HTML content for your 404 error page.
You can use the master page and include directives, read more about this here:
https://developers.docly.net/Blog/2014/Setting-up-and-using-a-Master-Page
The 404.hash file as never cached
This means that you can do database lookups and redirects from this page, to patch for old URL's etc.