I think you need to run Tools >> Network Setup first in your WP Admin if this is a new install?
This.
The problem is that WordPress doesn’t have any way to programmatically to activate Multisite in the database, so for SlickStack you have to comment out the Multisite constants in your wp-config.php
and then run the Tools >> Network setup first.
After that, uncomment those constants in wp-config.php
and you are good to go.
We probably need to find a way to emulate the WP-CLI commands:
wp core multisite-install
wp core multisite-convert