Creating user and group with cloud-config script

Hello. I am trying to create an ubuntu instance with a cloud-config script, that creates both of user and group at once. That is, I would like to create a user X whose primary group is X, and whose secondary groups is sudo, Y.

The following is what I gave as a cloud-config script:

#cloud-config
groups:
  - Y

users:
  - name: X
    groups: [ sudo, Y ]
    shell: /bin/bash
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    ssh-authorized-keys:
      - ssh-rsa xxx...xxx

runcmd:
  - echo "generated!!" > /home/X/test.txt

However, the group Y is not generated. Weirdly, the echo command is executed successfully. Are there any mistakes in my script?

Any guidance and pointers are welcome. Thanks in advance.