Multinetwork in subfolder

Hello guys

I’m trying to create a network giving wordpress a specific own folder.
But it doesn’t work. I’ve started from a fresh installation following these 2 guides:

1) https://codex.ww.wp.xz.cn/Giving_WordPress_Its_Own_Directory

2) https://codex.ww.wp.xz.cn/Create_A_Network

As soon as i modify my wp-config , i’ve the “error connecting to database”…if i revert wp-config.php to the old state, the site works but i’ve no network ofcourse