Have completely forgotten.
The setup always looks for the MySQLConfigFile.ini file in C:\Users\USERNAME\AppdData\Roaming\TestAPP\TestFolder\SQL 2014 SP2 Express , so I get an error that the file can't be found.
I have copied the file itself to make it work.
My Output Folder is: C:\Testpackage
and the MySQLConfigFile.ini is in C:\Testpackage\SQLServerExpr2014SP2
Where can I tell the software the right place of that .ini?
You can specify the path of the configuration file directly in the command line fields from the "Setup Files" tab of the prerequisite (e.g. /ConfigurationFile=[WindowsVolume]TestPackage\SQLServerExpr2014SP2).
Yes, you can use the "Additional Files" section to add your INI file, this is recommended. However, to tell the prerequisite to use that file, you need to send its path through command line as I suggested in the previous post. You can also see the conversations and test the sample from the previous page of this thread.