You can try this : 
-- Server --  
 
addEventHandler( 'onPlayerLogin', root, function( _, acc ) 
    if isObjectInACLGroup( 'user.'..getAccountName( acc ), aclGetGroup( "Admin" ) ) then 
        setElementData( source, 'OpenPanel', true) 
    else 
        setElementData( source, 'OpenPanel', nil)    
    end 
end 
) 
  
addEventHandler( 'onPlayerJoin', root, function() 
    setElementData( source, 'OpenPanel', nil) 
end ) 
 
-- Client --  
 
bindKey ("F6", "down", 
    function() 
        if getElementData( localPlayer, 'OpenPanel') ~= nil then     
            guiSetVisible(wnd, not guiGetVisible(wnd)) 
            showCursor(guiGetVisible(wnd)) 
            end 
        end  
) 
 
wnd = You're Window   
wnd will open only for admin group .