UrBackup docker container on QNAP NAS (QuTS Hero), some errors and questions

Hi!
I had problems with the UrBackup qpkg app (wont run after NAS firmware update / reboot), so i (try to) move to docker.
I have portainer installed but i couldn´t figure out, how to connect the container to the correct virtual switch of the NAS. I finally went with container station, created an app, pasted my customized version of the yaml file from https://hub.docker.com/r/uroni/urbackup-server in and the container was created successfully. I then modified the network in container station to my needs.
The container works, i can connect via ip:port.
In the protocol, there are some errors. For example: the test for zfs fails and i don´t understand why…

My docker compose file:

version: '2'

services:
  urbackup:
    image: uroni/urbackup-server:latest
    container_name: urbackup
    restart: unless-stopped
    environment:
      - PUID=1000 # Enter the UID of the user who should own the files here
      - PGID=100 # Enter the GID of the user who should own the files here
      - TZ=Europe/Stockholm # Enter your timezone
    volumes:
      - /share/backup/urbackup:/var/urbackup
      - /share/backup/urbackup:/backups
      # Uncomment the next line if you want to bind-mount the www-folder
      #- /path/to/wwwfolder:/usr/share/urbackup
    network_mode: "bridge"
    # Activate the following two lines for BTRFS support
    devices:
      - /dev/zfs:/dev/zfs

Docker protocol:

usermod: no changes
Raising nice-ceiling to 35 failed. (errno=1)
2024-08-06 14:48:54: Starting HTTP-Server on port 55414
2024-08-06 14:48:54: HTTP: Server started up successfully!
2024-08-06 14:48:54: Started UrBackup...
2024-08-06 14:48:54: Removing temporary files...
2024-08-06 14:48:54: Recreating temporary folder...
TEST FAILED: guestmount is missing (libguestfs-tools)
2024-08-06 14:48:54: Image mounting disabled: TEST FAILED: guestmount is missing (libguestfs-tools)
Testing for btrfs...
ERROR: not a btrfs filesystem: /backups/testA54hj5luZtlorr494
TEST FAILED: Creating test btrfs subvolume failed
Testing for zfs...
TEST FAILED: Dataset is not set via /etc/urbackup/dataset
2024-08-06 14:48:54: Backup destination cannot handle subvolumes and snapshots. Snapshots disabled.
2024-08-06 14:48:54: Reflink ioctl failed. errno=95
2024-08-06 14:48:55: InternetService: Server started up successfully!
2024-08-06 14:48:55: UrBackup Server start up complete.
2024-08-06 14:48:55: Server started up successfully!
2024-08-06 14:48:55: Looking for old Sessions... 0 sessions
2024-08-06 14:48:56: Downloading version file...
2024-08-06 14:49:00: Broadcasting on ipv4 interface eth0 addr 192.168.11.115
2024-08-06 14:49:06: ERROR: Error while downloading version info from http://update.urbackup.org/2.5.x/version.txt: Couldn't resolve host name(ec=6), Could not resolve host: update.urbackup.org
2024-08-06 14:49:06: Downloading version file...
2024-08-06 14:49:16: ERROR: Error while downloading version info from http://update.urbackup.org/2.5.x/version_linux.txt: Couldn't resolve host name(ec=6), Could not resolve host: update.urbackup.org
2024-08-06 14:49:16: Downloading server version info...
2024-08-06 14:49:25: Downloading dataplan database...

Can anybody help me understand / resolve the errors please?
I get that theres a problem with DNS, therefore URLs are not resolved and the downloads fail. Do i need to set the DNS server manually?
For the other errors, i have no idea…

Nevermind. It works in a full VM with NFS share.