@Viktor-Kanev, I had my friend with an iPhone try it. It worked for him. I suspect maybe you installed the Google Home app but maybe not the Google Assistant app yet?

@steven-canary, if your commands don't accept parameters, then whether your virtual switch is on or off, it just runs the command when you toggle the virtual switch on or off.

Or, in the SmartThings device handler code, you can remove the // in front of off(). That would make all of your virtual switches push buttons that automatically toggle themselves back off as soon you toggle them on.

// handle commands
def on() {
log.debug "Executing 'on'"
sendEvent(name:"switch",value:on)
parent.on(this)

}