Cannot create database/user in installation wizard

Hi community,
I am somehwat stuck in a installation of nextcloud 13.0.1 on Ubuntu 16.04 server.
I followed the installation guide on nextcloud’s webpage for the example configuration on an Ubunut system, which worked quite well until it was time to access the installation wizard, where I used the commandline version:

sudo -u www-data php occ maintenance:install --database “mysql” --database-name “obfuscated db-name” --database-user “root” --database-pass “obfuscated password for root” --admin-user “admin” --admin-pass “obfuscated password for admin”

This however leasds to the error message:
SQLSTATE[HY000][1698] Access denied for user ‘root’@‘localhost’

I did not create any batabases or database-users before. Could this be that root cause, that the database and a database user has already to be present for the installation wizard to work ?

Regards
Tobias

I always created database and user before, and created a dedicated user for the nextcloud database. Next I run the installation wizard with these credentials, not root.