Setting up your customizable 404 error page is straightforward.
1) Navigate to domain settings. Connect your domain and setup your 404 page under additional options
2) If you already have a domain setup, go to edit domain
3) Choose your 404/Error page
Note: Try to have a unique 404/Error page for a domain.
Once you've selected your custom 404/error page, users who encounter a 404 error on your site will automatically be redirected to your custom 404 page.