Error: String index out of range: 24?

[simoncn]

This is a known problem that is fixed in the latest MinimServer update (update 218). To install this update, select Properties from the minim icon in the macOS taskbar, then select Packages. You should see minimserver-update-218 listed in the Available packages box. Select this package, then click Install and follow the prompts. When the package has been installed successfully, click Relaunch. MinimServer should restart without this error.

I am not sure why this update was not installed automatically for you. MinimServer checks for online updates when it is started and automatically downloads and installs the latest available update. This should happen if an internet connection is available and you have not disabled automatic updates in the Properties dialog.