What CMS version are you using?
If you add a webpage that can be opened in the browser to the webpage module in Xibo, by default it’s in ‘Open natively’ mode, which means it will not be visible in the layout designer, but should work in preview and on a player.
Are you using Windows client? (what version?)
If so please also make sure you have IE11 installed and correct registry entries for browser emulation - Enabling HTML5 in the Windows .net Player