how to use cloud-init to install packages on a Raspberry pi 4?

After flashing the ubuntu-18.04.4-preinstalled-server-arm64+raspi3.img.xz image from https://ubuntu.com/download/raspberry-pi there is a file on the drive called user-data.

I'm trying to use that file to install some packages using instructions found on https://cloudinit.readthedocs.io/en/latest/topics/modules.html#package-update-upgrade-install

I added the following to the user-data file:

package_update: true

packages:
  - i2c-tools

After booting I see cloud-init using apt to update sources when it fails:

cloud-init[1549]: Err:14 http://ports.ubuntu.com/ubuntu-ports bionic-updates/universe arm64 arm64 1.0.0~rc7+git20190403.029124da-0ubuntu~18.04.2
cloud-init[1549]:    404 Not Found [IP: 91.189.88.150 80]
...

and it doesn't install the packages.

How do I use cloud-init to install packages?

Right after booting, I can log in and run sudo apt install i2c-tools and it works, so I'm connected to the Internet. (Ethernet btw)