Unable to assign property Text. string expected, got nil (?)

Hello! I am working on a simple DataStorage that saves the text the player put Inside of a textbox and loads It. The problem Is that when you are trying to load the data (Aka the textbox text) an error appears saying:

Unable to assign property Text. string expected, got nil

Slot script:

local slot = script.Parent
local LoadButton = slot.LoadButton
local SaveButton = slot.SaveButton
local LoadFunction = game.ReplicatedStorage:WaitForChild("LoadSlot")
local SaveEvent = game.ReplicatedStorage:WaitForChild("SaveSlot")
local Textbox = game.Players.LocalPlayer.PlayerGui:WaitForChild("TrollStorage").TextBox

SaveButton.MouseButton1Click:Connect(function()
    SaveEvent:FireServer(slot.Name, Textbox.Text)
end)

LoadButton.MouseButton1Click:Connect(function()
    local data = LoadFunction:InvokeServer(slot.Name)
    Textbox.Text = data
end)

ServerScriptService:

local SaveSlot = game:GetService("ReplicatedStorage").SaveSlot
local LoadSlot = game:GetService("ReplicatedStorage").LoadSlot
local Datastore = game:GetService("DataStoreService")
local slotStore = Datastore:GetDataStore("SlotStore")


function LoadSlot.OnServerInvoke(player, slot)
    return slotStore:GetAsync(player.Name.."-"..slot)
end

SaveSlot.OnServerEvent:Connect(function(player, slot, data)
    local Success = false
    while not Success do
        Success = pcall(function()
            slotStore:GetAsync(player.Name.."-"..slot, data)
        end)
    end
end)