C# Web API Sending Body Data in HTTP Post REST Client

You are not properly serializing your values to JSON before sending. Instead of trying to build the string yourself, you should use a library like JSON.Net.

You could get the correct string doing something like this:

var message = JsonConvert.SerializeObject(new {Password = pw, AppVersion = apv, AppComments = acm, UserName = user, AppKey = apk});
Console.WriteLine(message); //Output: {"Password":"password","AppVersion":"10","AppComments":"","UserName":"username","AppKey":"dakey"}

            var client = new RestClient("Your URL");
            var request = new RestRequest(Method.POST);
            request.AddHeader("Content-Type", "application/json");
            request.AddHeader("apk-key", apk);

            //Serialize to JSON body.
            JObject jObjectbody = new JObject();
            jObjectbody.Add("employeeName", data.name);
            jObjectbody.Add("designation", data.designation);

            request.AddParameter("application/json", jObjectbody, ParameterType.RequestBody);

            try
            {
                var clientValue= client.Execute<Response>(request);
                return RequestResponse<Response>.Create(ResponseCode.OK, "", clientValue.Data);
            }
            catch (Exception exception)
            {
                throw exception;
            }

I made a tools to do it quick and easy:

Install-Package AdvancedRestHandler

or

dotnet add package AdvancedRestHandler

AdvancedRestHandler arh = new AdvancedRestHandler("https://webapi.com/baseurl");
var result = await arh.PostDataAsync<MyLoginResponse, MyLoginRequest>("/login", new MyLoginRequest{
  Password = "password",
  AppVersion = "1",
  AppComments = "",
  UserName = "username",
  AppKey = "dakey"
});

public class MyLoginRequest{
  public string Password{get;set;}
  public string AppVersion{get;set;}
  public string AppComments{get;set;}
  public string UserName{get;set;}
  public string AppKey{get;set;}
}

public class MyLoginResponse {
  public string Token{get;set;}
}

Extra:

One other thing you can do is to use ArhResponse:

• Either this way, in the class definition:

public class MyLoginResponse: ArhResponse 
{
...
}

• Or this way, in the API call:

var result = await arh.PostDataAsync<ArhResponse<MyLoginResponse>, MyLoginRequest> (...)

and instead of try or cache, check your API call state using simple if statements:

// check service response status:
if(result.ResponseStatusCode == HttpStatusCode.OK) { /* api receive success response data */ }

// check Exceptions that may occur due to implementation change, or model errors
if(result.Exception!=null) { /* mostly serializer failed due to model mismatch */ }

// have a copy of request and response, in case the service provider need your request response and they think you are hand writing the service and believe you are wrong
_logger.Warning(result.ResponseText);
_logger.Warning(result.RequestText);

// Get deserialized verion of, one of the fallback models, in case the provider uses more than one type of data in same property of the model
var fallbackData = (MyFallbackResponse)result.FallbackModel;

Header Possible Issue

There are cases that the Server does not accept C# request due to the header that the HttpClient generates.

It is because HttpClient by default uses the value of application/json; charset=utf-8 for Content-Type...

For sending only application/json part as Content-Type and ignore the ; charset=utf-8 part, you can do as following:

For HttpClient you can fix it by looking into this thread: How do you set the Content-Type header for an HttpClient request?

As for (AdvancedRestHandler) ARH, I fixed it due to integration with some company, but I don't remember fully... I did it, either through options like of requests or through resetting the header value.

we will use HttpPost with HttpClient PostAsync for the issue.

using System.Net.Http;
    static async Task<string> PostURI(Uri u, HttpContent c)
    {
    var response = string.Empty;
    using (var client = new HttpClient())
    {
    HttpResponseMessage result = await client.PostAsync(u, c);
    if (result.IsSuccessStatusCode)
    {
    response = result.StatusCode.ToString();
    }
    }
    return response;
    }

We will call it by creating a string that we will use to post:

  Uri u = new Uri("http://localhost:31404/Api/Customers");
        var payload = "{\"CustomerId\": 5,\"CustomerName\": \"Pepsi\"}";

        HttpContent c = new StringContent(payload, Encoding.UTF8, "application/json");
        var t = Task.Run(() => PostURI(u, c));
        t.Wait();

        Console.WriteLine(t.Result);
        Console.ReadLine();