POST doesn't save nested field

When I POST this message :

    {
      "@context": "https://cdn.happy-dev.fr/owl/hdcontext.jsonld",
      "@id": "./",
      "description": "test 1",
      "skills": [
        {
          "@id": "http://127.0.0.1:8000/skills/1/"
        },
        {
          "@id": "http://127.0.0.1:8000/skills/2/"
        }
      ],
      "title": "test title"
    }

The object is created but without "skills".