Powershell - Show Messagebox by condition

snippet.ps1

<# This form was created using POSHGUI.com  a free online gui designer for PowerShell
.NAME
    Untitled
#>

Add-Type -AssemblyName System.Windows.Forms
[System.Windows.Forms.Application]::EnableVisualStyles()

$Form                            = New-Object system.Windows.Forms.Form
$Form.ClientSize                 = '400,400'
$Form.text                       = "Form"
$Form.TopMost                    = $false

$tb_payerid                      = New-Object system.Windows.Forms.TextBox
$tb_payerid.multiline            = $false
$tb_payerid.width                = 100
$tb_payerid.height               = 20
$tb_payerid.location             = New-Object System.Drawing.Point(135,60)
$tb_payerid.Font                 = 'Microsoft Sans Serif,10'

$Button1                         = New-Object system.Windows.Forms.Button
$Button1.text                    = "button"
$Button1.width                   = 60
$Button1.height                  = 30
$Button1.location                = New-Object System.Drawing.Point(161,144)
$Button1.Font                    = 'Microsoft Sans Serif,10'

$Form.controls.AddRange(@($tb_payerid,$Button1))

$Button1.Add_Click({ validate })




$Form.ShowDialog()

function validate(){

    if($tb_payerid.Text.Length -gt 0){

        [System.Windows.MessageBox]::Show('Missing Payer ID')
    }
}