So I've managed to find the magical item ID for 2 for 1 Zinger burgers. With a huge thanks to cooni as the original finder of this method of hacking the menu.
If the links open in your browser (not the app) and you just get a 404 Not Found error,
Long press the link and tap 'Open in "KFC"'. If this option isn't present, see if there's an app update available in the App Store.
click the Red KFC icon in the url box to get redirected to the KFC app
For color os / oppo users… heres how to adjust your app settings in order to use the links to take you directly to the app.