Attempt to index local hit a number value?

Your Problem

The MouseButton1Down event returns two values: The x and y coordinates of where you clicked on the UI element.

You are using the returned 'x' coordinate like it's the Player object.

Fix?

Reference the player by indexing the 'LocalPlayer' from game.Players - This will always return the player object when used from a LocalScript.

Note: Using meaningful variable names will help your code become neater and more legible.

local plr = game.Players.LocalPlayer; --This is the player object
local keycard = game.Lighting.Keycard --This is the keycard

--^Defined on the outside of the event because there's no need to define it everytime the event fires.

script.Parent.MouseButton1Down:Connect(function()
	local text = script.Parent.Parent.TextBox.Text
	local c = keycard:Clone() 
	local v = Instance.new("IntValue")
	v.Value = text
	v.Parent = c
	c.Parent = plr.Backpack
end)

Another note: Lighting is not meant for storage. Consider using ReplicatedStorage for this instead.