The window manager requires an Xorg server running, which creates a GUI display where windows can be managed.
-lite image does not include this GUI server software, although if you have installed a window manager it probably has been pulled in as a prerequisite. More on that at the end.
Create a file in the
$HOME of the user running the kiosk called
.xinitrc like this:
I'm presuming here the last line is the actual command you've been trying; if not use whatever that is.
This file may already exist if it is user
pi. If so just rename it to save a backup copy and create a new one.
The file should be created by the user, or else the ownership changed to match.
I think execute permissions are required on this, so then:
chmod a+x .xinitrc
Now as that user run
startx. If you get "command not found"
sudo apt install xinit. If it still does not work leave a comment.