Serializer not working on PUT / update

For instance :

{
  "@context": "https://cdn.happy-dev.fr/owl/hdcontext.jsonld",
  "@graph": [{
    "@id": ":b6114",
    "account": {"@id": ":b6115"},
    "chatProfile": {"@id": ":b6116"},
    "first_name": "Jean-Baptiste",
    "last_name": "Lemée"},
    {"@id": ":b6115",
      "picture": "https://pbs.twimg.com/profile_images/712730547588571136/NguMd0Fu_400x400.jpg"},
    {"@id": ":b6116",
      "jabberID": "jbl@happy-dev.fr"},
    {"@id": "http://127.0.0.1:8000/members/2/",
      "available": true,
      "bio": "Ma bio",
      "city": "Ma ville",
      "country": "France",
      "phone": "0687056019",
      "user": {"@id": ":b6114"},
      "website": "https://www.malt.com"}]}

does not serialize (@graph is ignored)