[Calgon]

pawn Код:

CMD:act(playerid, params[]) {
    if(isnull(params)) // check if anything was typed after "/act"
        return SendClientMessage(playerid,COLOR_WHITE,"Usage: /Act");
        
    if(!strcmp(params, "stop", true)) // check if what was typed was "stop"
        return 1;
    return 1;
}

Your command didn't contain much code to go off.