500 Internal Server Error during Installation

I want to install mautic on my ubuntu server with nginx.

I used the latest package (https://www.mautic.org/download/latest)
When I first load the page and the installer should start I get the following error message:

" Uh oh! I think I broke it. If I do it again, please report me to the system administrator!
500 Internal Server Error"

And the server log:


 mautic.CRITICAL: Uncaught PHP Exception Doctrine\DBAL\Exception\ConnectionException: "An exception occured in driver: SQLSTATE[HY000] [1045] Access denied for user ''@'localhost' (using password: NO)" at /usr/share/nginx/html/mautic/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php line 103 {"exception":"[object] (Doctrine\\DBAL\\Exception\\ConnectionException(code: 0): An exception occured in driver: SQLSTATE[HY000] [1045] Access denied for user ''@'localhost' (using password: NO) at /usr/share/nginx/html/mautic/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php:103, Doctrine\\DBAL\\Driver\\PDOException(code: 1045): SQLSTATE[HY000] [1045] Access denied for user ''@'localhost' (using password: NO) at /usr/share/nginx/html/mautic/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOConnection.php:47, PDOException(code: 1045): SQLSTATE[HY000] [1045] Access denied for user ''@'localhost' (using password: NO) at /usr/share/nginx/html/mautic/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOConnection.php:43)"} []

I also deleted the cache, but nothing changed.
Why there is a Access denied for user ‘’? This information should be set during the installation i guess. Any idea what’s going wrong here?