Alright, figured out how to get the Imaging Tool to work.
The USB Stick wasn’t found, because “Boot from USB” was disabled. Since then I got one Wyse working with a ThinOS 8.6 File, the others are getting error code 233. Which means, I don’t have the right version. But the question is, how do I get the Thin OS Lite Version as an Image?
Pulling the image/file from a working Wyse gave me the error code 300.
Any idea what to do next?