findOne method, the url and the database have the same userId but cannot acces to mongoose database

enter image description here

I use react for frontend.

Then I do a find method everything works perfecly. Now the I do findOne method that's another story, I always got in catch and 404 error.

router.get("/", auth, postCtrl.findFicheUser); // this routes works perfectly
router.get("/:id", auth, postCtrl.findSingleFicheUser);

exports.findSingleFicheUser = (req, res, next) => {
  console.log("req.params.id==>", req.params.id);
  // FicheUser.findById(req.params.id)
  FicheUser.findOne({ _id: req.params.id })

    .then((ficheUser) => {
      if (!ficheUser) {
        throw new Error("ficheUser not found");
      }
      console.log("ficheUser==>", ficheUser);
      res.status(200).json({ msg: "ficheUser found", ficheUser });
    })
    .catch((error) => {
      res.status(404).json({ msg: "ficheUser not found", error });
    });
};


//In react this is how I do my fetch 
const FicheUser = () => {
  const authCtx = useContext(AuthContext);

  // const { id } = useParams();
  // C'est quoi mon objectif: de passer les informations de ficheUser

  // recuperer tous les fichiers d'un userId
  // comment je fais pour acceder au ficheuser d'un userId
  const url = `http://localhost:3000/api/ficheUser/${authCtx.userId}`;
  // en faite ma route est tjs le meme ya pas le /:id

  const fetchHandler = async () => {
    try {
      const response = await fetch(url, {
        method: "GET",
        headers: {
          "Content-Type": "application/json",
          Authorization: `Bearer ${authCtx.token}`,
        },
      });

      const dataResponse = await response.json();

      if (response.ok) {
        console.log("dataResponse ==>", dataResponse);
      } else {
        throw new Error(
          `Failed to fetch data (${response.status}): ${dataResponse.message} `
        );
      }
    } catch (error) {
      console.log("Probleme serveur la req n'est pas parti");
      console.log(error);
    }
  };
 const isLoggedIn = authCtx.isLoggedIn;
  // console.log(isLoggedIn);

  if (isLoggedIn) {
    fetchHandler();
    // console.log()
  }

I get this in my console:
Probleme serveur la req n'est pas parti
FicheUser.js:39 Error: Failed to fetch data (404): undefined 
    at fetchHandler (FicheUser.js:33:1)
:7000/ficheUser/6414…4c1

This is my Mongo database _id: ObjectId('64148c621b64390be9b21ea2') userId:"64148befb3095018307b3840" age:1 nom:"" prenom:"test1" __v:0

I try the findOne method I expected that the params in the url and the userId of mongoDb matches. Instead geet a 404 error

ps: You can see in the image my userId matches.

I fixed my issue. It was in the line:

FicheUser.findOne({ _id: req.params.id })

it should be:

FicheUser.findOne({ _userId: req.params.id })

As you can see in the image I was matching the wrong id, instead of calling the userId I was calling the ficheUser's object.