Parse Server with Unity problems!

I’m trying to make new user signup using the SignUpAsync() method, and I’m getting this error:

ArgumentException: Input JSON was invalid.
Parse.Infrastructure.Utilities.JsonUtilities.Parse (System.String input) (at <b4991d8ca8744421a7f7ecfc48daa8ae>:0)
Parse.Infrastructure.Execution.ParseCommandRunner+<>c__DisplayClass17_0.<RunCommandAsync>b__1 (System.Threading.Tasks.Task`1[TResult] task) (at <b4991d8ca8744421a7f7ecfc48daa8ae>:0)
Rethrow as ParseFailureException: Invalid or alternatively-formatted response recieved from server.

and this is my code:

using System.Collections;

using System.Collections.Generic;

using UnityEngine;

using Parse;

using Parse.Infrastructure;

using System;

using System.IO;

using System.Threading.Tasks;

public class ParseServerTesting : MonoBehaviour

{

    // Start is called before the first frame update

    private ParseClient client;

    // Start is called before the first frame update

    async void Start()

    {

        #region Setup Client

        client = new ParseClient(new ServerConnectionData

        {

            ApplicationID = "001",//Real ones actually used

            ServerURI = "http://localhost:1337/server",

            Key = "DOTNETKEY", //Real ones actually used

            MasterKey = "123",//Real ones actually used

            Headers = new Dictionary<string, string>

            {

                ["x-parse-application-id"] = "001"

            }

        },

     new LateInitializedMutableServiceHub { },

     new MetadataMutator

     {

         EnvironmentData = new EnvironmentData { OSVersion = SystemInfo.operatingSystem, Platform = $"Unity {Application.unityVersion} on {SystemInfo.operatingSystemFamily}", TimeZone = TimeZoneInfo.Local.StandardName },

         HostManifestData = new HostManifestData { Name = Application.productName, Identifier = Application.productName, ShortVersion = Application.version, Version = Application.version }

     },

     new AbsoluteCacheLocationMutator

     {

         CustomAbsoluteCacheFilePath = $"{Application.persistentDataPath.Replace('/', Path.DirectorySeparatorChar)}{Path.DirectorySeparatorChar}Parse.cache"

     }

     );

        client.Publicize();

        Debug.Log("Client Created");

        ParseUser newUser = new ParseUser();

        newUser.Username = "Hameed";

        newUser.Password = "password";

        await client.SignUpAsync(newUser);

        #endregion

    }

}

I’d be surprised if the Parse .NET SDK would be working in an up-to-date environment. It’s not really maintained and the last release has been in 2016.