Testing for a game pass not working?

I am trying to make a game pass to set a player's int value (not for leaderboard) for a game where players can make their own obby. But whenever I run the script, it gives me this error message:

18:57:50.780 - Unable to cast value to Object

18:57:50.781 - Stack Begin

18:57:50.781 - Script 'Workspace.SaveObbySizeScript', Line 7

18:57:50.782 - Stack End

This is the code:

local datastore = game:GetService("DataStoreService")
local ds = datastore:GetDataStore("CashSaveSystem")

game.Players.PlayerAdded:connect(function(plr)
    local obbySize = Instance.new("IntValue", plr)
    obbySize.Name = "ObbySize"
    if game:GetService("GamePassService"):PlayerHasPass(plr.UserId, 4478771) then
        print("Success")
        obbySize.Value = 2000
        ds:SetAsync(plr.UserId, obbySize.Value)
    else
        obbySize.Value = ds:GetAsync(plr.UserId) or 300
        ds:SetAsync(plr.UserId, obbySize.Value)
    end


    obbySize.Changed:connect(function()
        ds:SetAsync(plr.UserId, obbySize.Value)
    end)
end)