Inivisble Rune

[Zuaro]

I want to make a invisible rune but it's not really good working...

Problems:
-Runes is infinite useable
-Magic level 20 is need and I want level 15 and no ML.
-It only haves to make you invisble for 5 minutes

function onUse(cid, item, frompos, item2, topos)
    --Config
    local reqml = 0         --Magic Level required to use it
    local reqlvl = 15       --Character Level required to use it
    local potExhaust = true    -- causes exhaust like potions (false creates seperate exhaust for mana rune)
    local ani = 12           --Animation to be sent to player when used (these can be found in your global.lua; search for CONST_ME_)
    local exhaustTime = 5       --Exhaust in seconds
    local infinite = false      --Will it cause rune to lose charges
    local canUseInPz = true    --If true, invisible rune may be used in PZ, otherwise, it will not work.

    local player_say = "Poof!"                            --What player says after successfully using the mana rune
    local error_ml = "You don't have the required magic level to use that rune."    --What the cancel says when ml is too low
    local error_lvl = "You don't have the required level to use this rune."   --What the cancel says when level is too low
    local error_notPlayer = "You can only use this rune on players."        --What the cancel says when you try to use it on something not a player
    local error_exhaust = "You are exhausted."                  --What the cancel says when you are exhausted
    ------------------------------------------- DO NOT EDIT BELOW THIS LINE!! -------------------------------------------

    ---------------------------START Check for Errors--------------------------------
    --If not high enough level, send poof and cancel message
    if getPlayerLevel(cid) < reqlvl then
        doSendMagicEffect(frompos, CONST_ME_POFF)
        doPlayerSendCancel(cid, error_lvl)
        return 0
    end

    --If ml is too low, send poof and cancel message
    if getPlayerMagLevel(cid) < reqml then
        doSendMagicEffect(frompos, CONST_ME_POFF)
        doPlayerSendCancel(cid, error_ml)
        return 0
    end
    --Check if exhausted
    if potExhaust == false then --If not using Potion Exhaust
        if exhaust(cid, storeValue, exhaustTime) == 0 then
            doSendMagicEffect(frompos, CONST_ME_POFF)
            doPlayerSendCancel(cid, error_exhaust)
            return 0
        end
    else --If you are using potion exhaust
        if hasCondition(cid, CONDITION_EXHAUSTED) == 1 then
            doPlayerSendCancel(cid, error_exhaust)
            return 0
        end
    end

    ---------------------------END Check for Errors--------------------------------

local combat = createCombatObject()
setCombatParam(combat, COMBAT_PARAM_EFFECT, CONST_ME_MAGIC_RED)
setCombatParam(combat, COMBAT_PARAM_AGGRESSIVE, 0)

function onCastSpell(cid, var)
	return doCombat(cid, combat, var)
end

--Exhaust System created by Alreth
--Edited by OsoSangre
function exhaust(cid, storeValue, exhaustTime)
    local newExhaust = os.time()
    local oldExhaust = getPlayerStorageValue(cid, storeValue)
    if (oldExhaust == nil or oldExhaust < 0) then
        oldExhaust = 0
    end
    if (exhaustTime == nil or exhaustTime < 0) then
        exhaustTime = 1
    end
    diffTime = os.difftime(newExhaust, oldExhaust)
    if (diffTime >= exhaustTime) then
        setPlayerStorageValue(cid, storeValue, newExhaust)
        return 1
    else
        return 0
    end
end

Can Someone help me?