Error: 400 - {"message":"Invalid json data"} While using Post method in Unity

I am trying to send a PUT request using UnityWebRequest to update game data on a server. However, I keep getting the error:

css Copy Edit Error: 400 - {"message":"Invalid json data"} I have tested the same JSON in Postman, and it works correctly. But when sending it from Unity, the request fails with a 400 Bad Request error.

API's request sample

'{
    "gameId": "93bdd165-51aa-4aab-87c2-516a234465b9",
    "used": {
        "startBoosts": [
            {
                "name": "Head start",
                "quantity": 8
            },
            {
                "name": "Score multiplier",
                "quantity": 4
            }
        ],
        "normalBoosts": [
            {
                "name": "Magnet",
                "quantity": 8
            },
            {
                "name": "Force Shield",
                "quantity": 6
            },
            {
                "name": "Hyperdrive",
                "quantity": 1
            }
        ]
    },
    "collected": [
        {
            "name": "Magnet",
            "quantity": 1
        },
        {
            "name": "Force Shield",
            "quantity": 0
        },
        {
            "name": "Hyperdrive",
            "quantity": 3
        }
    ],
    "finalScore": 36598521
}'

json (string) generated in unity before uploading within the PUT method request

Generated JSON: {
  "gameId": "8eb97e75-8127-47e9-abd5-895e094b4e32",
  "used": {
    "startBoosts": [
      {
        "name": "Head start",
        "quantity": 0
      },
      {
        "name": "Score multiplier",
        "quantity": 0
      }
    ],
    "normalBoosts": [
      {
        "name": "Magnet",
        "quantity": 0
      },
      {
        "name": "Force Shield",
        "quantity": 0
      },
      {
        "name": "Hyperdrive",
        "quantity": 0
      }
    ]
  },
  "collected": [
    {
      "name": "Magnet",
      "quantity": 0
    },
    {
      "name": "Force Shield",
      "quantity": 0
    },
    {
      "name": "Hyperdrive",
      "quantity": 0
    }
  ],
  "finalScore": 0
}

Code:

private IEnumerator SendDeclareGameEndRequest()
{
    // Ensure BoostsManager is set
    BoostsManager boostsManager = FindObjectOfType<BoostsManager>();

    if (boostsManager == null)
    {
        Debug.LogError("BoostsManager not found!");
        yield break;
    }

    // Get game data
    GameEndData gameEndData = boostsManager.GetGameEndData(gameId, score.score);

    // Convert to JSON using Newtonsoft.Json
    string json = JsonConvert.SerializeObject(gameEndData, Formatting.Indented);

    Debug.Log("Generated JSON: " + json); // Debugging output

    byte[] jsonToSend = System.Text.Encoding.UTF8.GetBytes(json);

    using (UnityWebRequest request = new UnityWebRequest(apiUrl, "PUT"))
    {
        request.uploadHandler = new UploadHandlerRaw(jsonToSend);
        request.downloadHandler = new DownloadHandlerBuffer();

        request.SetRequestHeader("session-token", sessionToken);
        request.SetRequestHeader("Content-Type", "application/json");

        yield return request.SendWebRequest();

        if (request.result == UnityWebRequest.Result.Success)
        {
            Debug.Log("Game End Declared Successfully: " + request.downloadHandler.text);
        }
        else
        {
            Debug.LogError("Error: " + request.responseCode + " - " + request.downloadHandler.text);
        }
    }
}

Debugging Steps Taken

• Checked the generated JSON in Unity logs and verified it matches Postman.
• Ensured Content-Type is correctly set to application/json.
• Tried sending data as a string instead of a byte[], but UnityWebRequest requires byte[] for PUT.
• Used both Unity’s built-in JsonUtility and Newtonsoft.Json for serialization.