Sending json through api post request

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C#

ASP.NET

JSON

API

I'm currently struggling to send a JSON via post request into my controller to use it further by calling a stored procedure.

Here is the post request using axios:

async returnJSON(model) {
      this.info = await axios.post(
          "https://localhost:44349/api/items/AddItem/",model)
        .then((response) => response.data);

Here is the structure of model

{
  "arrayAutori": [
    {
      "dinUniversitate": true,
      "creatorType": 4,
      "creatorID": 3
    }
  ],
  "itemID": "",
  "itemTypeID": 6,      
  "drepturiDeAutor": {
    "valueID": "",
    "fieldID": 15
  },
  "isbn": {
    "valueID": "",
    "fieldID": 25
  },
  "limba": {
    "valueID": "",
    "fieldID": 7
  },
  "numarPagini": {
    "valueID": "",
    "fieldID": 43
  },
  "data": {
    "valueID": "",
    "fieldID": 6
  },
  "editura": {
    "valueID": "",
    "fieldID": 23
  },
  "editie": {
    "valueID": "",
    "fieldID": 42
  },
  "volum": {
    "valueID": "",
    "fieldID": 19
  },
  "numarColectie": {
    "valueID": "",
    "fieldID": 41
  },
  "titlu": {
    "valueID": "",
    "fieldID": 1
  }
}

And here is my controller:

public string AddItem( JObject jsonString)
       {
           db.Database.ExecuteSqlCommand("exec zotero.PublicationsMerge " + jsonString);
           db.SaveChanges();
           return "1";
       }

What I have tried:

I can not make a model class to use it, because that JSON may vary depending on the publications. Also, when I'm debugging this controller, jsonString looks like this:

{{
  "arrayAutori": [
    {
      "dinUniversitate": true,
      "creatorType": 4,
      "creatorID": 3
    }
  ],
  "itemID": "",
  "itemTypeID": 6,
  "drepturiDeAutor": {
    "valueID": "",
    "fieldID": 15
  },
  "isbn": {
    "valueID": "",
    "fieldID": 25
  },
  "limba": {
    "valueID": "",
    "fieldID": 7
  },
  "numarPagini": {
    "valueID": "",
    "fieldID": 43
  },
  "data": {
    "valueID": "",
    "fieldID": 6
  },
  "editura": {
    "valueID": "",
    "fieldID": 23
  },
  "editie": {
    "valueID": "",
    "fieldID": 42
  },
  "volum": {
    "valueID": "",
    "fieldID": 19
  },
  "numarColectie": {
    "valueID": "",
    "fieldID": 41
  },
  "titlu": {
    "valueID": "",
    "fieldID": 1
  }
}}

I don't know why, but it adds another pair of {}. What am I doing wrong?