How do I save tables into Datastore? [SOLVED]

I am trying to save levels and xp to the player but this errors on line 18

-- Variables
local xp_lvl_DataStore = game:GetService('DataStoreService'):GetDataStore('xp/lvlStore')
local xpLvlTable = {}
local repStorage = game:GetService('ReplicatedStorage')
local xp_lvlFunction = repStorage:WaitForChild('Xp_LvlFunction')

-- Events
-- Gets xp and lvl stats
local success,message = pcall(function()
    xp_lvlFunction.OnServerInvoke = function(plr)
        local key = 'Player-'..plr.UserId
        -- Checks if player has data that can be sent
        if xp_lvl_DataStore:GetAsync(key) then
            return xp_lvl_DataStore:GetAsync(key)
        else
            -- sets the xp to 0 if plr is new
            local xpLvlTable = table.insert(xpLvlTable,0,0)
            xp_lvl_DataStore:SetAsync(key,(xpLvlTable))
            return xp_lvl_DataStore:GetAsync(key)
        end
    end
end)

error: Argument 2 missing or nil