I am trying to make a Datastore to save Maps in my game, but it gives me this error. Any help?

I am currently fixing one of my games' Map Datastore, but when I leave the game it keeps giving me this error in the output:

104: Cannot store Instance in data store. Data stores can only accept valid UTF-8 characters.  -  Server

I have absolutely no idea what this means and there are no youtube videos or developer articles about this.

This is the script for my Map Datastore. The Datastore Script itself is located in the ServerScriptService.

local datastoreService = game:GetService("DataStoreService")
local rs = game:GetService("ReplicatedStorage")

local map2Datastore = datastoreService:GetDataStore("Map2Datastore_A")
local map3DataStore = datastoreService:GetDataStore("Map3Datastore_A")
local map4Datastore = datastoreService:GetDataStore("Map4Datastore_A")
local map5DataStore = datastoreService:GetDataStore("Map5Datastore_A")

game.Players.PlayerAdded:Connect(function(plr)
    local mapsFolder = Instance.new("Folder")
    mapsFolder.Name = "MapsFolder"
    mapsFolder.Parent = plr

    local map2Value = Instance.new("IntValue")
    map2Value.Name = "Map2Value"
    map2Value.Parent = mapsFolder

    local map3Value = Instance.new("IntValue")
    map3Value.Name = "Map3Value"
    map3Value.Parent = mapsFolder

    local map4Value = Instance.new("IntValue")
    map4Value.Name = "Map4Value"
    map4Value.Parent = mapsFolder

    local map5Value = Instance.new("IntValue")
    map5Value.Name = "Map5Value"
    map5Value.Parent = mapsFolder


    local MapData2
    local MapData3
    local MapData4
    local MapData5

    local success, errormessage = pcall(function()
        MapData2 = map2Datastore:GetAsync(plr.UserId.."-map2")
        MapData3 = map3DataStore:GetAsync(plr.UserId.."-map3")
        MapData4 = map4Datastore:GetAsync(plr.UserId.."-map4")
        MapData5 = map5DataStore:GetAsync(plr.UserId.."-map5")
    end)

    if success then
        map2Value.Value = MapData2
        map3Value.Value = MapData3
        map4Value.Value = MapData4
        map5Value.Value = MapData5
    else
        print("There was an error MapDatastore.")
        warn(errormessage)
    end
end)

game.Players.PlayerRemoving:Connect(function(player)
    local success, errormessage = pcall(function()
        map2Datastore:SetAsync(player.UserId.."-map2", player.MapsFolder.Map2Value)
        map3DataStore:SetAsync(player.UserId.."-map3", player.MapsFolder.Map3Value)
        map4Datastore:SetAsync(player.UserId.."-map4", player.MapsFolder.Map4Value)
        map5DataStore:SetAsync(player.UserId.."-map5", player.MapsFolder.Map5Value)
    end)

    if success then
        print("Successfully saved Map Data!")
    else
        print("There was an error while saving Map Data!")
        warn(errormessage)
    end
end)

Any help on this?