Please Help I Am Struggling

[SkyMining]

command /sc [<text>]:
    trigger:
        if arg-1 is set:
            make player execute command "/staffchat %arg-1%"
        if arg-1 is not set:
            cancel event
        make player execute command "/staffchat"

im getting this error

[_Tarna_]

That isn't an event. So you can't cancel it. If you want it to do nothing if arg-1 isn't set, just don't have that if statement. It will automatically do nothing since you have a previous if statement checking if arg-1 is set. Or make arg-1 required so the player has to specify arg-1 in order for the command to run.