Project directory ... is not empty

I try to install Contao 4.8 on XAMPP. I have downloaded contao-manager.phar and added .php to it. Placed the file in /htdocs/contao/web folder. Edited the corresponding DocumentRoot. Downloaded and activated composer.phar - placed in the /htdocs/ folder.
I have given complete permissions to the /contao and subfolders.

I open XAMPP-control.exe as administrator
When I run php composer.phar create-project contao/managed-edition /contao/web 4.8
I get [InvalidArgumentException]
Project directory /contao/web/ is not empty.

Have done this many times. Same respons

The /contao/web/ folder is empty except for contao-manager.phar.php

I have tried lots o different ways - placed the contao-manager.phar.php in different folders, running the composer.phar from different folders. At one moment I succeeded to start the install but it was blocked because of too little memory. I gave more memory but I did not have this respons again. Every other time I only get the "directory not empty".

I have tried to clean the Chrome cache. I have deleted the /contao/web/ folders and recreated them.

I have tried to access the localhost:IP/contao/web/contao-manager.phar.php through the browser but get The object was not found.

HELP!!