I have an issue starting a container using key files pair.

I have the following error
unable to parse RSA public key: invalid key: Key must be a PEM encoded PKCS1 or PKCS8 key

Here is the mercure part of my docker-compose

  mercure:
    image: dunglas/mercure
    restart: unless-stopped
    ports:
      - "5500:80"
    environment:
      SERVER_NAME: ":80"
      MERCURE_PUBLISHER_JWT_KEY: $(cat /certs/private.pem)
      MERCURE_PUBLISHER_JWT_ALG: 'RS256'
      MERCURE_SUBSCRIBER_JWT_KEY: $(cat /certs/public.pem)
      MERCURE_SUBSCRIBER_JWT_ALG: 'RS256'
      MERCURE_EXTRA_DIRECTIVES: 'cors_origins http://localhost:5100 http://localhost:5101 http://localhost:5103'
      GLOBAL_OPTIONS: 'debug'
      DEBUG: 1
    networks:
      - backend
    volumes:
      - mercure_data:/data
      - mercure_config:/config
      - ./config/jwt:/certs

I tried to change the MERCURE_*_JWT_KEY to "/certs/private.pem" directly and event to inline the content in a YAML block (starting with "|") but I have the same error.
My key pair files are valid PKCS8 key, the headers are -----BEGIN PRIVATE KEY----- and -----BEGIN PUBLIC KEY-----

when I docker compose up the container, it keep restarting so i can't check anything inside.

Edit : I kinda made it work by inlining the public key for both publisher and subscriber. I don't know wherte I saw I should use the private key for the publisher but id doesn't work.
Though i can't use file, I have to inline it.