The default or static pages to customize are located in : /sentora/panel/etc/static/ OR /zpanel/panel/etc/static/ depending on your installation.

Customizing these pages can be a valuable tool with helping to promote your business or products! (View default example here or custom example here)
Post specials, coupons, information about your company, pretty much anything you want!

There are a few pages you can customize: Hosting Space is ready (welcome.html), Parked Domains, Bandwidth Exceeded, Storage Space Exceeded, Error Pages, etc. (Basically all pages in the /panel/etc/static/ folder can be customized.)

The error pages will be copied to your client's hosting space when a new domain or subdomain is created as well as the welcome.html will be placed in their domain's root folder as index.html.

After customizing them, I suggest backing them up to another folder so that when you do an upgrade in the future you can just replace them instead of having to remake them all over again.

Click here to read more about customizing the Error Pages