Unable to configure network with preseed file

Incus
1

I am trying to configure a incus instance using a preseed file. The plan is to run a simple mariadb instance in a container as a test. I cannot seem to correctly configure my network in a way that it is accessable to the outside world. Logging into the database from the container works fine. I can see my port open, and a local connection to the db works great:

[root@nixos:~]# netstat  -tuplen                                                                                                                                            
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       User       Inode      PID/Program name    
tcp        0      0 0.0.0.0:3306            0.0.0.0:*               LISTEN      84         161839     512/mysqld          
tcp6       0      0 :::3306                 :::*                    LISTEN      84         161840     512/mysqld          
tcp6       0      0 :::22                   :::*                    LISTEN      0          151309     1/systemd           
udp        0      0 0.0.0.0:68              0.0.0.0:*                           999        161795     437/dhcpcd: [manage 
udp6       0      0 :::546                  :::*                                999        161836     437/dhcpcd: [manage

Outside the container, I cannot seem to connect to the instance when it has its default configuration:
(included for reference:)

$> incus profile show default
config: {}
description: Default Incus profile
devices:
  eth0:
    name: eth0
    network: incusbr-1000
    type: nic
  root:
    path: /
    pool: default
    type: disk
name: default
used_by:
- /1.0/instances/lxcTest-container?project=user-1000
project: user-1000

And I cannot try to modify the default profile so that it works properly.
When I try to run

incus init lxcTest-aaimage-8b90e8 lxcTest-container < /nix/store/bprz29fqxk8lwkqv1zaym463npyi5iy9-preseed.yaml

I receive a parser error:

 Error: yaml: unmarshal errors:
  line 13: cannot unmarshal !!map into string

The generated yaml is valid json:

{
  "networks": [
    {
      "config": {
        "ipv4.address": "auto",
        "ipv6.address": "auto"
      },
      "name": "lxdbr0",
      "type": "bridge"
    }
  ],
  "profiles": [
    {
      "devices": {
        "eth0": {
          "name": "eth0",
          "network": "lxdbr0",
          "type": "nic"
        },
        "root": {
          "path": "/",
          "pool": "default",
          "type": "disk"
        }
      },
      "name": "default"
    }
  ],
  "storage_pools": [
    {
      "config": {
        "source": "[redacted path]"
      },
      "driver": "dir",
      "name": "default"
    }
  ]
}

But, in a attempt to diagnose, I also tried writing it out in the yaml style just in case:

    networks:
    - name: incusbr0
      type: bridge
      config:
        ipv4.address: 10.250.76.0
        ipv4.nat.address: 10.250.76.10
        ipv6.address: none
    storage_pools:
    - name: data
      driver: dir
      config:
        source: ${secrets.lxcStore}
    profiles:
    - name: default
      devices: 
        root:
          path: /
          pool: data
          type: disk
        eth0:
          name: eth0
          network: incusbr0
          type: nic

This also failed to parse.

Error: yaml: unmarshal errors:
  line 15: cannot unmarshal !!map into string

TL; DR
Two problems:

  1. Can’t find the external address to log into the container (probably super straighforward but I’m stuck anyways)
  2. Can’t configure profiles in my preseed.yaml due to parsing errors.

My environment is entirely configured using NixOS, so I can also include the full reproducible nix setup if you think it would help.

Incus version 6.0.3.