please help me i am getting error "attempt to index number with 'Start' "?

Can anyone help me i am making a tower defence simulator and when i spawn more than 1 wave it gives me an error "attempt to index number with 'Start' "

i have a part in the workspace in my folder 'Grassland' which is my map and this is my wave code

local mob = require(script.Mob) local map = workspace.Grassland

for wave=1,2 do print("WAVE STARTING:", wave)

if wave <= 1 then
	mob.Spawn("Zombie", 3 * wave, map)
elseif wave <= 2 then
	mob.Spawn("Zombie", 6, wave, map)
	mob.Spawn("FastZombie", 3, wave, map)
elseif wave == 2 then
	mob.Spawn("Zombie", 100, map)
end

repeat
	task.wait(1)
until #workspace.Mobs:GetChildren() == 0

print("WAVE ENDED")
task.wait(13)

end

and this is my main script

local PhysicsService = game:GetService("PhysicsService") local ServerStorage = game:GetService("ServerStorage") local mob = {}

function mob.Move(mob, map) local humanoid = mob:WaitForChild("Humanoid") local waypoints = map.Waypoints

for waypoint=1, #waypoints:GetChildren() do
	humanoid:MoveTo(waypoints[waypoint].Position)
	humanoid.MoveToFinished:Wait()
end

mob:Destroy()

end

function mob.Spawn(name, quantity, map) local mobExists = ServerStorage.Mobs:FindFirstChild(name)

if mobExists then
	for i=1, quantity do
		task.wait(0.5)
		local newMob = mobExists:Clone()
		newMob.HumanoidRootPart.CFrame = map.Start.CFrame
		newMob.Parent = workspace.Mobs
		newMob.HumanoidRootPart:SetNetworkOwner(nil)
		
		for i, object in ipairs(newMob:GetDescendants()) do
			if object:IsA("BasePart") then
				PhysicsService:SetPartCollisionGroup(object, "Mob")
			end
		end
		
		
		coroutine.wrap(mob.Move)(newMob, map)
	end
	
else
	warn("Request mob doesnt exists", name)
end

end

return mob