Why is my while loop not spawning zombies?

It says that on line 5 the random interval is empty

the part1 and part 2 are max and low

local Repeatloop = 20
local Enemy = game.ServerStorage.Enemies["Red Button"]

while Repeatloop > 0 do
	local xpos = math.random(game.Workspace.Part1.Position.X,game.Workspace.Part2.Position.X)
	local ypos = math.random(game.Workspace.Part1.Position.Z,game.Workspace.Part2.Position.Z)
	local zombie = Enemy:Clone()
	local Placement = zombie.HumanoidRootPart.Position
	zombie.Parent = game.Workspace
	Placement = Vector3.new(xpos, 3, ypos)
	wait(1)
	Repeatloop -= 1
end