Import real world terrain into Roblox

RealWorldTerrainRoblox.lua

--[[
Steps:

1. Download heightmap Bitmap
    e.g. from terrain.party: http://terrain.party/api/export?name=guarda&box=10.186055,46.850130,10.080975,46.778264)
    e.g. from earthe
      Data Sets: NASA LPDAAC Collections -> NASA SRTM (SRTM 3) Collections
2. Use this site to convert BMP to Lua: https://codepen.io/Domiii/pen/oMJvoJ?editors=0010
3. Copy the final Lua code to workspace.TerrainPixels (ModuleScript)
4. Run this script!

]]

local MaxHeight = 1800
local VoxelSize = 1
local MaxPixelValue = 255
local Resolution = 1      -- only use every 4th pixel

-- xLen = 100
-- zLen = 100


local VoxelVectorSize = Vector3.new(VoxelSize, VoxelSize, VoxelSize)
local origin = Vector3.new(0, 0, 0)

function GenerateMountain(origin, xLen, zLen, height)
  for i = 1, xLen do
    for j = 1, zLen do
      local y = math.random() * height
      --print(y)
      for k = 1, y do
        --local size = Vector3.new(Amount*Amount-(i*10),Y*(i*2),Amount*Amount-(i*10))
        --local pos = pos + Vector3.new(i * VoxelSize, k*VoxelSize, j*VoxelSize)
        local pos = origin + Vector3.new(i*VoxelSize, k*VoxelSize, j*VoxelSize)
        game.Workspace.Terrain:FillBlock(CFrame.new(pos), VoxelVectorSize, Enum.Material.Rock)
      end
    end
  end
end


local cancelName = 'TerrainCancel'
local guiName = 'TerrainGenStatusGui'
local cancelledRef
local gui
local statusLabel

function Cleanup()
  if game.StarterGui:FindFirstChild(guiName) then
    game.StarterGui:FindFirstChild(guiName):Destroy()
  end
  if workspace:FindFirstChild(cancelName) then
    workspace:FindFirstChild(cancelName):Destroy()
  end
end

function GetProgressPercent(current, max)
  return current / max * 100
end

function UpdateStatus(current, max)
  local progressPct = GetProgressPercent(current, max)
  statusLabel.Text = tostring(math.floor(progressPct + 0.5)) .. '%'
end

function ShowTerrainGui()
  gui = Instance.new('ScreenGui')
  gui.Name = guiName
  statusLabel = Instance.new('TextLabel')
  statusLabel.Parent = gui
  statusLabel.Size = UDim2.new(1, 0, 0, 30)
  gui.Parent = game.StarterGui

  cancelledRef = workspace:FindFirstChild(cancelName)
  if not cancelledRef then
    cancelledRef = Instance.new('BoolValue')
    cancelledRef.Name = cancelName
    cancelledRef.Parent = workspace
  end
  cancelledRef.Value = false

  -- select the Cancel object
  local select = { cancelledRef }
  game.Selection:Set(select)
end

function CheckCancel()
  if cancelledRef and cancelledRef.Value then
    print('Terrain Generation Cancelled')
    Cleanup()
    return true
  end
  return false
end

function GetMaterial(yNormalized)
  local material
  if yNormalized < 0.4 then
    material = Enum.Material.Grass
  elseif yNormalized < 0.8 then
    material = Enum.Material.Rock
  else
    material = Enum.Material.Snow
  end
  return material
end


function GenTerrainFromHeightmap(origin)
  local pixels = require(workspace.TerrainPixels:Clone())
  
  local xLen = #pixels
  local zLen = #pixels[1]

  Cleanup()
  ShowTerrainGui()

  workspace.Terrain:Clear()

  for i = 1, xLen, Resolution do
    local row = pixels[i]
    for j = 1, zLen, Resolution do

      local px = row[j]
      local yNormalized = px / MaxPixelValue
      local material = GetMaterial(yNormalized)

      y = yNormalized * MaxHeight

      --for k = 1, y do
      local pos = origin + Vector3.new(i*VoxelSize, 0, j*VoxelSize)
      local size = Vector3.new(VoxelSize, y * VoxelSize, VoxelSize)
      
      game.Workspace.Terrain:FillBlock(CFrame.new(pos), size, material)
      --end
    end
    if CheckCancel() then return end
    UpdateStatus(i, xLen)
    wait()
  end

  print('Terrain Generation Finished!')
  Cleanup()
end

--GenTerrainFromHeightmap(origin, pixels)
--GenerateMountain(origin, xLen, zLen, height)

function GenTerrainBetweenParts(basePart)
  Cleanup()
  ShowTerrainGui()

  workspace.Terrain:Clear()

  local material = Enum.Material.Grass
  local size = basePart.Size
  local pos1 = basePart.Position - size / 2
  local pos2 = pos1 + size
  local y = basePart.Position.Y + size.Y
  --local y = (pos1.Y + pos2.Y) / 2
  local up = Vector3.new(0, 1, 0)

  for z = pos1.Z, pos2.Z do
    for x = pos1.X, pos2.X do
      local origin = Vector3.new(x, y, z)
      local ray = Ray.new(origin, origin + up * 100000)
      local terrainCellsAreCubes = false
      local ignoreWater = true
      local part, pos, normal, material2 = workspace:FindPartOnRay (
        ray,
        basePart,
        terrainCellsAreCubes,
        ignoreWater
      )

      --print(x,y,z, part, pos, normal, material2)
      -- local p = Instance.new('Part')
      -- p.Shape = Enum.PartType.Ball
      -- p.Position = origin
      -- p.Parent = workspace.Tmp

      --if part then
      local blockSize = Vector3.new(1, (pos - origin).Y, 1)
      -- NOTE: basePos is the center of the block!
      local basePos = origin + blockSize/2
      game.Workspace.Terrain:FillBlock(CFrame.new(basePos), blockSize, material)
      --end
    end

    if CheckCancel() then return end
    UpdateStatus(z-pos1.Z, pos2.Z-pos1.Z)
    wait()
  end

  print('Terrain Generation Finished!')
  Cleanup()
end

GenTerrainBetweenParts(workspace.Baseplate)

It says
The current identity (2) cannot Set (lacking permission 1)
What is wrong?