I used this:

version: "3"

services:

sliding-proxy:
image: ghcr.io/matrix-org/sliding-sync:v0.99.1
restart: unless-stopped
ports:
- "127.0.0.1:8881:8881"
environment:
- "SYNCV3_SECRET="
- "SYNCV3_SERVER=DOMAIN.ltd
- "SYNCV3_DB=user=syncv3 dbname=syncv3 sslmode=disable host=sliding-postgres password=hunter2"
- "SYNCV3_BINDADDR=0.0.0.0:8881"
depends_on:
- sliding-postgres
networks:
- synapse_default

sliding-postgres:
image: docker.io/postgres:15-alpine
restart: unless-stopped
environment:
- "POSTGRES_USER=syncv3"
- "POSTGRES_PASSWORD=hunter2"
- "POSTGRES_DB=syncv3"
volumes:
- /volume2/docker/slidingsync/sliding_db_data:/var/lib/postgresql/data
networks:
- synapse_default

volumes:
sliding_db_data:

networks:
synapse_default:
external: true
name: synapse_default

You might want to add your example in a markdown code block.

Anyhow. I think such an example should be added to the git repo.

I needed to convert the instructions to docker-compose too. Here's the formatted version of the above comment, with some typos corrected and deprecated version line removed.

services:
  sliding-proxy:
    image: ghcr.io/matrix-org/sliding-sync:v0.99.1
    restart: unless-stopped
    ports:
      - "127.0.0.1:8881:8881"
    environment:
      - "SYNCV3_SECRET="
      - "SYNCV3_SERVER=DOMAIN.tld"
      - "SYNCV3_DB=user=syncv3 dbname=syncv3 sslmode=disable host=sliding-postgres password=hunter2"
      - "SYNCV3_BINDADDR=0.0.0.0:8881"
    depends_on:
      - sliding-postgres
    networks:
      - synapse_default

  sliding-postgres:
    image: docker.io/postgres:15-alpine
    restart: unless-stopped
    environment:
      - "POSTGRES_USER=syncv3"
      - "POSTGRES_PASSWORD=hunter2"
      - "POSTGRES_DB=syncv3"
    volumes:
      - /volume2/docker/slidingsync/sliding_db_data:/var/lib/postgresql/data
    networks:
      - synapse_default

volumes:
  sliding_db_data:

networks:
  synapse_default:
    external: true
    name: synapse_default

I needed to convert the instructions to docker-compose too. Here's the formatted version of the above comment, with some typos corrected and deprecated version line removed.

services:
  sliding-proxy:
    image: ghcr.io/matrix-org/sliding-sync:v0.99.1
    restart: unless-stopped
    ports:
      - "127.0.0.1:8881:8881"
    environment:
      - "SYNCV3_SECRET="
      - "SYNCV3_SERVER=DOMAIN.tld"
      - "SYNCV3_DB=user=syncv3 dbname=syncv3 sslmode=disable host=sliding-postgres password=hunter2"
      - "SYNCV3_BINDADDR=0.0.0.0:8881"
    depends_on:
      - sliding-postgres
    networks:
      - synapse_default

  sliding-postgres:
    image: docker.io/postgres:15-alpine
    restart: unless-stopped
    environment:
      - "POSTGRES_USER=syncv3"
      - "POSTGRES_PASSWORD=hunter2"
      - "POSTGRES_DB=syncv3"
    volumes:
      - /volume2/docker/slidingsync/sliding_db_data:/var/lib/postgresql/data
    networks:
      - synapse_default

volumes:
  sliding_db_data:

networks:
  synapse_default:
    external: true
    name: synapse_default

Thanks. Create a PR Plz ;)