@Diego-Ulises-Pérez-Ruiz, maybe you need to specify the full path to nircmd.exe in your command, like c:\tools\nircmd.exe ...
Also, by manually, I assume you mean when you run it manually from the command line it works. What if you run it manually via TRIGGERcmd using the green Trigger button on the website, or from the green Play arrow in the GUI Editor ? We should make sure those work before attempting Alexa.