Can't call method from module?

I just starting to learn about OOP and make this script(module):

local Part = {}
Part._index = Part

function Part.Create(name, parent, size, position)
	local part = {newPart = Instance.new("Part")}
	setmetatable(part , Part)
	
	part.newPart.Name = name
	part.newPart.Parent = parent
	part.newPart.Size = size
	part.newPart.Position = position
	
	return part
end

function Part:ChangeColor(color)
	self.newPart.BrickColor = color
end

return Part

Another script:

local Part = require(game:GetService("ReplicatedStorage").CreatePart)

script.Parent.MouseClick:Connect(function()
	local newPart = Part.Create("Stuff", game:GetService("Workspace"), Vector3.new(2, 2, 2), Vector3.new(0, 2, 0))
 --Part.Create(name, parent, size, position)
	newPart:ChangeColor(BrickColor.new("Bright green")) --change the BrickColor of newPart
end)

The first function is work, but the second one can't. When I try to use the function, it throw this error:

Workspace.Button.ClickDetector.Script:5: attempt to call method 'ChangeColor' (a nil value)

Thank for reading :D

On line 5 you have part instead of Part. Double check your code as lua is case sensitive:

local Part = require(game:GetService("ReplicatedStorage").CreatePart)

script.Parent.MouseClick:Connect(function()
    local part = Part.Create("Stuff", game:GetService("Workspace"), Vector3.new(2, 2, 2), Vector3.new(0, 2, 0))
    Part:ChangeColor(BrickColor.new("Bright green"))
end)