Vagrant: * Unknown configuration section 'disk

During the configuration of Vagrant environment on my machine I've received this message:

Vagrant: * Unknown configuration section 'disksize'.

It was shown after the plugin has already been installed.

Here is the vagrantfile:

# -*- mode: ruby -*-
# vi: set ft=ruby :
# All Vagrant configuration is done below. The "2" in Vagrant.configure
# configures the configuration version (we support older styles for
# backwards compatibility). Please don't change it unless you know what
# you're doing.
Vagrant.configure("2") do |config|
  # The most common configuration options are documented and commented below.
  # For a complete reference, please see the online documentation at
  # https://docs.vagrantup.com.
  # Every Vagrant development environment requires a box. You can search for
  # boxes at https://atlas.hashicorp.com/search.

  config.vm.box = "bento/ubuntu-16.04"
  config.disksize.size = '150GB'
  config.vm.provider :virtualbox do |vb|
  vb.gui = true
  end

  # Disable automatic box update checking. If you disable this, then
  # boxes will only be checked for updates when the user runs
  # `vagrant box outdated`. This is not recommended.
  # config.vm.box_check_update = false

  # Create a forwarded port mapping which allows access to a specific port
  # within the machine from a port on the host machine. In the example below,
  # accessing "localhost:8080" will access port 80 on the guest machine.

  config.vm.network "forwarded_port", guest: 8888, host: 8887

  # Create a private network, which allows host-only access to the machine
  # using a specific IP.

  config.vm.network :private_network, ip: "192.168.33.12"
  config.vm.hostname = "dsvm"

  # Create a public network, which generally matched to bridged network.
  # Bridged networks make the machine appear as another physical device on
  # your network.
  # config.vm.network "public_network"

  # Share an additional folder to the guest VM. The first argument is
  # the path on the host to the actual folder. The second argument is
  # the path on the guest to mount the folder. And the optional third
  # argument is a set of non-required options.

  config.vm.synced_folder "./shared_directory", "/shared_directory"

  # Provider-specific configuration so you can fine-tune various
  # backing providers for Vagrant. These expose provider-specific options.
  # Example for VirtualBox:
  #
  config.vm.provider "virtualbox" do |vb|
    # Display the VirtualBox GUI when booting the machine
    #vb.gui = true

    # Customize the amount of memory on the VM:
    vb.memory = "4096"#"2048"
    vb.customize ["modifyvm", :id, "--cableconnected1", "on"]

  end

  # View the documentation for the provider you are using for more
  # information on available options.

  # Define a Vagrant Push strategy for pushing to Atlas. Other push strategies
  # such as FTP and Heroku are also available. See the documentation at
  # https://docs.vagrantup.com/v2/push/atlas.html for more information.
  # config.push.define "atlas" do |push|
  #   push.app = "YOUR_ATLAS_USERNAME/YOUR_APPLICATION_NAME"
  # end

  # Enable provisioning with a shell script. Additional provisioners such as
  # Puppet, Chef, Ansible, Salt, and Docker are also available. Please see the
  # documentation for more information about their specific syntax and use.

  #config.ssh.username = 'root'
  #config.ssh.password = 'vagrant'
  #config.ssh.insert_key = 'true'

  #fixing_scripts
  config.vm.provision :shell, path: "./shared_directory/install_scripts/fixing_scripts.sh"

  #install_various_tools
  config.vm.provision :shell, path: "./shared_directory/install_scripts/install_various_tools.sh"

  #install_java
  config.vm.provision :shell, path: "./shared_directory/install_scripts/install_java.sh"

  #finalize_instalations.sh
  config.vm.provision :shell, path: "./shared_directory/install_scripts/finalize_instalations.sh"

  # Install R:  
  config.vm.provision :shell, path: "./shared_directory/install_scripts/install_R.sh"

  # Install Docker: 
  config.vm.provision :shell, path: "./shared_directory/install_scripts/install_docker.sh"

  # Adjust size :   
  config.vm.provision :shell, path: "./shared_directory/install_scripts/adjust_size_1.sh"
  config.vm.provision :shell, path: "./shared_directory/install_scripts/adjust_size_2.sh"

  #config.vm.provision "shell", inline: <<-SHELL
    # some bach commnads to run in 1st "vagrant up"   
  #SHELL

  config.vm.provision "shell", run: "always", inline: <<-SHELL
    sudo su -
    source /root/.bashrc
    sudo -H jupyter notebook --notebook-dir=/shared_directory --no-browser --ip=0.0.0.0 --port=1565 &

  SHELL
  #Vagrant.configure("2") do |config|
  #  config.vm.provision "chef_solo" do |chef|
  #      chef.add_recipe 'apt'
  #      chef.add_recipe ''
  #  end
  #end

end

I've tried changing the capacity of disksize.size to a smaller size, but without success.

What could be the problem?

Thanks in advance

You need to install the plugin: