WebAPI giving GET method error when called in browser

[HttpPost]
public void AddEmployee(Employee employee)
{
//int maxId = listEmp.Max(e => e.ID);
//employee.ID = maxId + 1;
//listEmp.Add(employee);


SqlConnection myConnection = new SqlConnection();
myConnection.ConnectionString = @"Server=192.168.200.26;Database=DBCompany;User ID=abc;Password=1234;";
//SqlCommand sqlCmd = new SqlCommand("INSERT INTO tblEmployee (EmployeeId,Name,ManagerId) Values (@EmployeeId,@Name,@ManagerId)", myConnection);
SqlCommand sqlCmd = new SqlCommand();
sqlCmd.CommandType = CommandType.Text;
sqlCmd.CommandText = "INSERT INTO tblEmployee (EmployeeId,Name,ManagerId) Values (@EmployeeId,@Name,@ManagerId)";
sqlCmd.Connection = myConnection;


sqlCmd.Parameters.AddWithValue("@EmployeeId", employee.EmployeeId);
sqlCmd.Parameters.AddWithValue("@Name", employee.Name);
sqlCmd.Parameters.AddWithValue("@ManagerId", employee.ManagerId);
myConnection.Open();
int rowInserted = sqlCmd.ExecuteNonQuery();
myConnection.Close();
}

using System;
using System.Collections.Generic;
using System.Text;

namespace TestWebAPIConsume
{
    class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public int ManagerId { get; set; }
    }
}

protected void Page_Load(object sender, EventArgs e)
        {
            
            HttpClient client = new HttpClient();
            string serviceUrl = "http://localhost/WebApiDemo/api/Employees/AddEmployee";
            var Employee = new Employee()
            {
                EmployeeId = 44,
                Name = "AmitKumar",
                ManagerId = 21
            };
            try
            {
                HttpResponseMessage response = client.PostAsJsonAsync(serviceUrl, Employee).Result;
                if (response.IsSuccessStatusCode)
                {
                    Console.WriteLine("EmployeeAdded");
                }
                else
                {
                    Console.WriteLine("{0}({1})", (int)response.StatusCode, response.ReasonPhrase);
                }
            }
            
            catch (Exception ex) {
                lblmsg.Text= ex.Message.ToString();
            }
        }