how to pass complex object parameters in postman?

my c# api takes two parameters, one complex object and one string:

[HttpPost, Route("paramtester")]
public string paramtester(people user, string message) {
    return user.name + message;}

how do I pass by a json object in the body? I have tried passing in a serial json object which doesn't work at all:

{
    "user": {
        "name": "John Doe",
        "age": 30,
        "country": "USA"
    },
    "message": "Hello, World!"
}

this will return:

{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "00-40ce97917410bdcff73bb4d8737ed944-2c7f4bf20348d6b7-00",
    "errors": {
        "name": [
            "The name field is required."
        ],
        "address": [
            "The address field is required."
        ],
        "message": [
            "The message field is required."
        ]
    }
}

There is 2 correct approaches:

1. create a request object that contains a complex object user and a silple string message

   public class ParamTesterRequest
   {
      public People User {get; set;}
      public string Message {get; set;}
   }
   

   So your web API become

    [HttpPost("paramtester")]
    public string ParamTester(ParamTesterRequest request)
    {
       return request.User.Name + request.Message;
    }
   

2. the other one is as said by Selvin, use the complex parameter user from body and the other one as query parameter. So your web API become

    [HttpPost("paramtester")]
    public string ParamTester([FromQuery] string message, [FromBody] People user)
    {
       return user.Name + message;
    }
   

NOTE: the first answer is that it is the simplest and cleanest

You should create a DTO (Data Transfer Object) that includes both:

    public sealed class MyDto
    {
        [JsonPropertyName("user")]
        public User user { get; set; }

        [JsonPropertyName("message")]
        public string message { get; set; }
    }

    public sealed class User
    {
        [JsonPropertyName("name")]
        public string name { get; set; }

        [JsonPropertyName("age")]
        public int age { get; set; }

        [JsonPropertyName("country")]
        public string country { get; set; }
    }

Then add [FromBody] to the endpoint:

[HttpPost, Route("paramtester")]
public string paramtester([FromBody] MyDto myDto) {
    return myDto.Name + myDto.Message;}