Can't assign bodyposition position y value to basepart position y value

Don’t really know why exactly this isn’t working, but I’m trying to get a model that’s cloned into the workspace to change its bodyposition y position to the primary part (of the model) y position (after the model is placed into workspace via placement system); instead I get the Y cannot be assigned to error.

script.Parent.Parent.AncestryChanged:Connect(function(_, parent)
	if parent == workspace.Constructables then
		script.Parent.BodyPosition.Position.Y = script.Parent.Position.Y + 3
		print("position set")
	end
end)

image

Can anyone tell me how I can fix this?

You have to do

script.Parent.BodyPosition.Position = Vector3.new(script.Parent.BodyPosition.Position.X, script.Parent.BodyPosition.Position.Y + script.Parent.Position.Y + 3, script.Parent.BodyPosition.Position.Z)