Failed binding ipv6 socket to port 35623

I have a working server on docker compose that backups a windows machine. i would like to create a docker compose client on a different machine however when i deploy the image i get the following errors;

ERROR: urbackupserver: Failed binding ipv6 socket to port 35623. Another instance of this application may already be active and bound to this port.
urbackupserver: Server started up successfully!
Started UrBackupClient Backend...
Backing up volume /backup
Looking for old Sessions... 2 sessions
Final path: /backup
Final path: /backup

this is my docker compose for the client;

    image: uroni/urbackup-client:latest
    container_name: urbackup-client
      - "35623:35623"
      - TZ=Europe/London
      - URBACKUP_SERVER_NAME=urbackup://********:55414
      - URBACKUP_CLIENT_NAME=Docker-V8-Media
      - /mnt/General_Storage/Backups/Server_Apps/Urbackup/:/backups

ive checked out the other ranking topics on this matter, their solutions were related to “already had one installed” which is not the case here, every docker machine ive tried this on fails

can anyone help with this? am i missing some information that would help?