Years ago, I made a program with Autoit3 to turn off the monitors of any PC I was connected to remotely, Autoit3 can turn off any one or more monitors on a PC natively with no third-party solution needed although, if I recall correctly, it will need to be run as administrator. I recommend this post to get started.
It's nothing technical, it looks like the application start without being aware of the passed argument. Try using numerical arguments (see the previous post).