Nvidia Flex install problem

When I try to install the Flex branch (or any other branch, like the VR editor) I get the following error while running the setup.bat file

It says: Failed to download [long string of letters and numbers] The stated filepath and/or filename is to long. The fully qualified filename has to be shorter than 260 characters and the filename shorter than 248 characters.
Press any key to continue

After pressing any key thebatchfile just closes.

This problem also occurred with the setup for the UE4 VR editor…

Try to move the project to C:\ (root directory)

Could it be that I do not fully understand the installation process?
I thought, that it was like a normal install (like an addon to the engine)
Do I have to install this to projects or the engine itself.

Could you please explain the installation step by step? Because I do not fully understand the instructions on the git hub page

You’re about to install a full copy of Unreal Engine, not only an addon.

Hi J.R.

Unfortunately we do not directly support the Nvidia Flex branch of the Engine. That branch was created, and is maintained, by Nvidia. As Xi4 mentioned, you may want to try unzipping the source code to a location closer to the root location of your drive.

When you download the Engine source code from GitHub, you are getting everything you need to build the Engine yourself. It is not an addon or plugin that you can drop into an existing installation of the Engine. It gives you more flexibility and control over what you can do with the Engine, but requires a little more setup work. For more information about getting started with building the Engine from source code, you can see this page.