Insert data through Asp.net web API in sql server database

I am trying to insert data using web API. I have taken empty web application with Web API folder and core references.

My AppModel Class

public class AppModel
{
    public int RegisterId { get; set; }

    public string RegisterName { get; set; }

    public string RegisterUserName { get; set; }

    public string RegisterPassword { get; set; }

    public string RegisterEmail { get; set; }

    public string RegisterMobile { get; set; }

    public DateTime RegisterDate { get; set; }

    public string RegisterStatus { get; set; }
}

Below is my HomeController code

namespace RestfulWebApi.Controllers
{
public class HomeController : ApiController
{
    SqlConnection xc;
    SqlCommand xcmd;

    [HttpPost]
    public string RegisterUser([FromBody] AppModel register)
    {
        try
        {
            using (xc = new SqlConnection(ConfigurationManager.ConnectionStrings["db_appConnectionString"].ConnectionString))
            {
                xcmd = new SqlCommand("sp_insert_register", xc);
                xcmd.CommandType = CommandType.StoredProcedure;
                xcmd.Parameters.AddWithValue("@register_id", register.RegisterId);
                xcmd.Parameters.AddWithValue("@register_name", register.RegisterName);
                xcmd.Parameters.AddWithValue("@register_username", register.RegisterUserName);
                xcmd.Parameters.AddWithValue("@register_password", register.RegisterPassword);
                xcmd.Parameters.AddWithValue("@register_email", register.RegisterEmail);
                xcmd.Parameters.AddWithValue("@register_mobile", register.RegisterMobile);
                xcmd.Parameters.AddWithValue("@register_date", DateTime.Now);
                xcmd.Parameters.AddWithValue("@register_status", "True");

                xc.Open();
                int i = xcmd.ExecuteNonQuery();
                if (i > 0)
                {
                    msg = "User Registered";
                }
                else
                {
                    msg = "Something went wrong.";
                }

            }
        }
        catch (Exception ex)
        {
            msg = ex.ToString();
        }

        return msg;
    }
}

}

I am confused how to pass values to these parameter.I am testing API in Postman. I don't what key to pass in Body