Well, i checked after modifying the configuration.php file, and using the primary database, and it's user. It works, right. But you write you changed the user. Where did you change ? I do not see. Or may be you went back to initial config? Did you make any other changes?
So, i don't understand eveything, but it seems it works with either databases, and the initial user and password.
I will go on, change http to https. Up to you, should i remove my second database and use the one you worked on?
Regards
jluc