if you select the action, your script will only start on your client. The other clients won't notice it.
isServer only checks if you're the server. This is not the case if you're not the host. So your code will be skipped and not executed.
To execute the command on the server, define a boolean variable, add a PublicVariableEventHandler to the variable via the init file and only on the server.
This handler will execute your code you currently have in your action.
Then you modify the action to toggle the variable and broadcast it via publicVariable.
At the time the server will get the modified variable, he will run your code for the action.
A small downside is left: The handler won't fire if the publicVariable was executed on the same client. See the Biki comment on this. So you need a small modification to make sure that the new code will work on hosted sessions.
And I would recommend to inform yourself about the locality of commands and the effect.
It's important to know these for multiplayer scripting.