That was the password I used. Unfortunately, this didn't work.
I also tried creating a new MySQL user with full privileges, creating the database with this user and logging in, via the server, with those credentials. Still, it did not work.
I am thinking it maybe the server setup which is not compatible. Of course, that's just a guess.
I tried setting up as described on the GitHub page under installation (still with Digital Ocean's LAMP one-click install), but I get the same result.