Seems as if the mysql root login details in the ispconfig mysql_clientdb.conf file were not correct or contained any special chars which might get interpreted by shell scripts so the mysql dunp could not be loaded into the database.
Check the file
it has to contain the valid root user login details and the password shall not contain special chars that might be interpreted on the shell.
If the above requirements are met, then rerun the ispconfig installation script.
The next thing is that the latest billing mdule requires ispconfig 3.0.5. Please ensure that you installed ispconfig 3.0.5 or 126.96.36.199 before you install the billing module.
The "billing" option has appeared on the user modules page, but not in the main menu.
You have to enable the billing module for the admin user under System > CP users (please see installation instructions in the billing module manual for details).