"You must enter the details of an existing account" but Db is created!

Nas ds712+ / DSM 6.2.4

Mariadb10/php7/webStation : Install ok (tested with a personal website)

But with “nextcloud” I have the following error message:
“Invalid MySQL database username and/or password You must enter the details of an existing account.”

But this account exists and moreover the database I indicate in the form is create by this form after clicking “install”. So there is no pb of access to MariaDb.

I don’t know what/where to look for. Does anyone have a clue?

I’m happy to answer to myself!
I simply stop using camelCases in Database name and username.
bddNext => bddnext.
The installation starts, stops with a 504 but create tables, I try again and its ok.
I’m now connected.