What is problem in codes (send message)

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VB

I'm trying to develop some code to do a button click onto an application without moving the cursor over to it. I can see messages under Spy++ but nothing happens.
Thanks in advance...

Public Class Form1
    Const WM_LBUTTONDOWN = &H201
    Const WM_LBUTTONUP = &H202
    Const MK_LBUTTON = &H1
    Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As Int32) As Int32
    Declare Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Int32
    Private Sub cmdBSPerform_Click(sender As Object, e As EventArgs) Handles cmdBSPerform.Click
        Dim hwnd As Long = FindWindow(vbNullString, handle.Text)
        Dim lParam As Int32
        lParam = MakeLParam(txtXBSPerform.Text, txtYBSPerform.Text)
        SendMessage(hwnd, WM_LBUTTONDOWN, WM_LBUTTONUP, MakeLParam(txtXBSPerform.Text, txtYBSPerform.Text))
        SendMessage(hwnd, WM_LBUTTONUP, 0, MakeLParam(txtXBSPerform.Text, txtYBSPerform.Text))
    End Sub
    Public Function MakeLParam(ByVal LoWord As Int32, ByVal HiWord As Int32) As Int32
        Return (HiWord << 16) Or (LoWord And &HFFFF)
    End Function
End Class

What I have tried:

I tried do a button click onto an application without moving the cursor over to it, I can see my messages under spy++ but nothing happens