qgis-server Service HELLO is not registered

Question

I want to build a qgis-server plugin and I started with the "HelloWorld" example and I get an error "Service HELLO is not registered" in the container logs, although the server response is as expected "hello server".

I followed the steps as described in the official documentation:

I deployed qgis-server on a docker container using this dockerfile: https://docs.qgis.org/3.34/en/docs/server_manual/containerized_deployment.html#simple-docker-images

And adapted this example to my docker environment: https://docs.qgis.org/3.34/en/docs/server_manual/plugins.html#manually-with-a-zip

This is my docker compose service:

  qgis_server:
    build:
      context: ./qgis_server
      dockerfile: Dockerfile
    volumes:
      - ./qgis_server/data:/home/qgis/data
      - ./qgis_server/plugin:/home/qgis/plugins
    ports:
      - 8050:80
    environment:
      QGIS_PROJECT_FILE: /home/qgis/data/osm.qgs
      QGIS_PLUGINPATH: /home/qgis/plugins
    networks:
      - my_net

The plugin is in "./qgis_server/plugin". This is the url in my environment : http://localhost:8050/qgis-server/?SERVICE=HELLO

browser result image

I get a proper "Hello Server" response but in the container logs :

2024-03-17 14:28:45 13:28:45 CRITICAL Server[22]: Service HELLO is not registered

error log in docker container

This is the full log :

2024-03-17 22:24:07 QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
2024-03-17 22:24:07 Warning 1: Unable to find driver ECW to unload from GDAL_SKIP environment variable.
2024-03-17 22:24:07 Warning 1: Unable to find driver ECW to unload from GDAL_SKIP environment variable.
2024-03-17 22:24:07 Warning 1: Unable to find driver JP2ECW to unload from GDAL_SKIP environment variable.
2024-03-17 22:24:07 "Loading native module /usr/lib/qgis/server/liblandingpage.so"
2024-03-17 22:24:07 "Loading native module /usr/lib/qgis/server/libwcs.so"
2024-03-17 22:24:07 "Loading native module /usr/lib/qgis/server/libwfs.so"
2024-03-17 22:24:07 "Loading native module /usr/lib/qgis/server/libwfs3.so"
2024-03-17 22:24:07 "Loading native module /usr/lib/qgis/server/libwms.so"
2024-03-17 22:24:07 "Loading native module /usr/lib/qgis/server/libwmts.so"
2024-03-17 22:24:07 <frozen importlib._bootstrap_external>:629: DeprecationWarning: find_module() is deprecated and slated for removal in Python 3.12; use find_spec() instead
2024-03-17 22:24:07 <frozen importlib._bootstrap_external>:1591: DeprecationWarning: FileFinder.find_loader() is deprecated and slated for removal in Python 3.12; use find_spec() instead
2024-03-17 22:24:07 <frozen importlib._bootstrap>:283: DeprecationWarning: the load_module() method is deprecated and slated for removal in Python 3.12; use exec_module() instead
2024-03-17 22:29:41 21:29:41 CRITICAL Server[22]: Service HELLO is not registered

What am I missing ?