Paywall: error 500 when I add a website

[oldDuB98]

Version: 2.6.14
Installation: Installed to Docker on both Synology and UGreen NAS, with Portainer.
PHP version: NSP
OS: Synology DSM 7 / UGreen OS
Database: MariaDB (the one install with the standard deployment script)
Parameters:

services:
  wallabag:
    image: wallabag/wallabag
    container_name: Wallabag
    restart: on-failure:5
    environment:
      - MYSQL_ROOT_PASSWORD=wallaroot
      - SYMFONY__ENV__DATABASE_DRIVER=pdo_mysql
      - SYMFONY__ENV__DATABASE_HOST=db
      - SYMFONY__ENV__DATABASE_PORT=3306
      - SYMFONY__ENV__DATABASE_NAME=wallabag
      - SYMFONY__ENV__DATABASE_USER=wallabag
      - SYMFONY__ENV__DATABASE_PASSWORD=wallapass
      - SYMFONY__ENV__DATABASE_CHARSET=utf8mb4
      - SYMFONY__ENV__DOMAIN_NAME=http://xxx.xxx.xxx.xxx:6749
      - SYMFONY__ENV__SERVER_NAME=xxxxxxxxx
      - SYMFONY__ENV__FOSUSER_CONFIRMATION=false
      - SYMFONY__ENV__FOSUSER_REGISTRATION=true
      - SYMFONY__ENV__TWOFACTOR_AUTH=true
    ports:
      - 6749:80
    volumes:
      - /volume1/docker/wallabag/images:/var/www/wallabag/web/assets/images:rw
      - /volume1/docker/wallabag/data:/var/www/wallabag/data:rw
    depends_on:
     - db
     - redis
  db:
    image: mariadb:11.4-noble #LTS Long Time Support Until May 29, 2029.
    container_name: Wallabag-DB
    restart: always
    environment:
      - MYSQL_ROOT_PASSWORD=wallaroot
      - TZ=Europe/Paris
    volumes:
      - /volume1/docker/wallabag/db:/var/lib/mysql:rw
      
  redis:
    image: redis:alpine
    container_name: Wallabag-REDIS
    healthcheck:
     test: ["CMD-SHELL", "redis-cli ping || exit 1"]
    volumes:
      - /volume1/docker/wallabag/redis:/data:rw
    restart: on-failure:5

I tried to fix permissions error (chmod 664) but still the same. (I follow explanation given for the similar issue "Paywall: error 500 when I add a website wallabag/wallabag#3477" reported as "closed").
NB : the file "site-credentials-secret-key.txt" wasn't created during program installation nor after having activated the paywall parameter (set to '1'). I created myself with command line and ensure it was then created in data directory.

[Kdecherf]

Hi @oldDuB98,

It is unclear what is the exact error message you hit while receiving this 500 error page.
Could you check the content of /var/www/wallabag/var/log/prod.log?