Curtin does not use preseeds in /var/snap/maas/current/preseeds (snap)

Snap install of JuJu- I've made this file:

# cat /var/snap/maas/current/preseeds/curtin_userdata
#cloud-config
debconf_selections:
 maas: |
  {{for line in str(curtin_preseed).splitlines()}}
  {{line}}
  {{endfor}}

early_commands:
   disable_reboot: touch /run/block-curtin-poweroff /tmp/block-poweroff /tmp/block-reboot

late_commands:
# maas: [wget, '--no-proxy', '{{node_disable_pxe_url}}', '--post-data', '{{node_disable_pxe_data}}', '-O', '/dev/null']
  99_install_packages: ['curtin', 'in-target', '--',
                        'env', 'DEBIAN_FRONTEND=noninteractive',
                        'apt-get', 'install', '-qy',
                        'net-tools locate chrony ifupdown vlan bridge-utils']

This file does not appear to be used when I deploy. The unit does reboot, and does not install the packages.

MAAS: 3.0.0

Following instructions from here: https://www.programmersought.com/article/41894334170/