Add external frontends/backends with docker labels working

Hey everyone !
I currently have an issue configuring a use case.
I have two devices on my network, all requests going to my first device.
And I would like to let some of the requests go trough and to my second device.

Let imagine we have the first one having the ip 10.0.0.10 and the second 10.0.0.20

The first have a docker-compose initializing a traefik and some services with labels. The point is to add a backend for redirecting to 10.0.0.20.

I tried the following but it doesn't work :

version: "3.4"
  
  services:
    reverse-proxy:
      image: traefik:1.7
      env_file: 
        - .env
      command: --api --docker --acme.email="${ACME_EMAIL}"
      container_name: traefik
      volumes:
        - /var/run/docker.sock:/var/run/docker.sock
        - ./traefik.toml:/etc/traefik/traefik.toml
        - ./acme.json:/acme.json
      labels:
        - traefik.frontend.rule=Host:${TRAEFIK_DASHBOARD_HOST}
        - traefik.port=8080
      networks:
        - proxy
      expose:
        - 8080
      ports:
        - 80:80
        - 443:443
      restart: unless-stopped
    vscode:
      image: linuxserver/code-server
      container_name: vscode
      env_file: .env
      environment:
        PUID: ${PUID}
        PGID: ${PGID}
        TZ: ${TIMEZONE}
        PASSWORD: ${PASSWORD}
        SUDO_PASSWORD: ${PASSWORD}
      labels:
        - traefik.backend=vscode
        - traefik.frontend.rule=Host:${VSCODE_HOST}
        - traefik.frontend.auth.basic=${HTACCESS}
        - traefik.docker.network=proxy
        - traefik.port=8443
      volumes:
        - ${VSCODE_CONFIG}:/config
        - ${PROJECT_DIR}:/projects
      ports:
        - "8443"
      networks:
        - proxy
      restart: unless-stopped

  networks:
    proxy:
      external:
        name: proxy

This part is working juste fine but then I add those lines in my toml :

[backends]
  [backends.backend1]
    [backends.backend1.servers.server1]
    url = "http://10.0.0.20:80"
    weight = 1

[frontends]
  [frontends.frontend1]
  backend = "backend1"
    [frontends.frontend1.routes.route1]
    rule = "Host:test.example.com"

And traefik doesn't add it when starting..
Could someone tell me how to do that and especially tell me if it is possible ?

Thanks !