[C#] Mouse Move nur in Form

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace lolhiddenbugclickftw
{
    public partial class Form1 : Form
    {
        public const int WM_LBUTTONDOWN = 0x0201;
        public const int WM_LBUTTONUP = 0x0202;

        [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
        [DllImport("user32.dll")]
        public static extern IntPtr PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

        Thread rpThread;

        private static IntPtr MakeLParam(int LoWord, int HiWord)
        {
            return (IntPtr)((HiWord << 16) | (LoWord & 0xffff));
        }

        public Form1()
        {
            InitializeComponent();
            rpThread = new Thread(new ThreadStart(giveRP));
        }

        private void button1_Click(object sender, EventArgs e)
        {
            rpThread.Start();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            rpThread.Abort();
        }

        private void giveRP()
        {
            while (true)
            {
                // Payment Method
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(226, 408));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(226, 408));
                Thread.Sleep(1000);
                // Price
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(812, 263));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(812, 263));
                Thread.Sleep(5000);
                // ToU
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(503, 339));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(503, 339));
                // Remember
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(503, 358));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(503, 358));
                // Continue - 1
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(743, 278));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(743, 278));
                Thread.Sleep(5000);
                // Continue - 2
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(644, 301));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(644, 301));
                Thread.Sleep(5000);
                // Back
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONDOWN, IntPtr.Zero, MakeLParam(639, 416));
                PostMessage(FindWindow("ApolloRuntimeContentWindow", "PVP.net Client"), WM_LBUTTONUP, IntPtr.Zero, MakeLParam(639, 416));
                Thread.Sleep(5000);
            }
        }
    }
}