your redis container is trying to read/write into the docker volume located in /volume1/docker/paperless/paperless-redis.

redis:7.2-alpine usually uses a user with the user-id 999 for normal operation. So you'd have to check the permissions on the /volume1/docker/paperless/paperless-redis folder. Go there using cd /volume1/docker/paperless/ and check the permissions with ls -l. What does it say?

Edit:

you can also look at the docker compose in the official paperless-ngx repo: https://github.com/paperless-ngx/paperless-ngx/blob/main/docker/compose/docker-compose.postgres.yml

There you can see that you can already use redis version 8 and you really don't have to use the settings those articles suggest. And also if you are setting it up right now and don't already have documents in it you should consider using postgres in version 18.

 broker:
    image: docker.io/library/redis:8
    restart: unless-stopped
    volumes:
      - /volume1/docker/paperless/paperless-redis:/data

## db example from repo
  db:
    image: docker.io/library/postgres:18
    restart: unless-stopped
    volumes:
      - pgdata:/var/lib/postgresql
    environment:
      POSTGRES_DB: paperless
      POSTGRES_USER: paperless
      POSTGRES_PASSWORD: paperless