OnServerEvent not working for Transformation?

When I was testing a transformation code (Using Z to transform with remote events & Toolbox Localscripts, with an execution script in the workspace) I came across a large issue. When I used "OnServerEvent", it said "OnServerEvent" is not a valid member of script. When testing this with a fireball using similar if not the exact same script, minus casting time and cooldown, it worked.

    Player = game.Players.LocalPlayer
Transforming = false
Transformed = false



 game.Workspace.Powerup.OnServerEvent:Connect(function(Player, Debounce)

if Transformed == true then

Player.Character.Humanoid.MaxHealth = 100

Transformed = false

else

local Character = Player.Character or Player.CharacterAdded:wait()

Transforming = true

local Aura = Instance.new("Part", Player.Character.UpperTorso)

Aura.Transparency = 1

Aura.Anchored = true

local Aurafire = Instance.new("ParticleEmitter", Aura)

Aurafire.Texture = ("rbxassetid://242102147")

Aurafire.Color = BrickColor.new("Black")

wait(5)

Player.Character.Humanoid.MaxHealth = 200

Transforming = false

Transformed = true

end

end)