Update DataGridView via button click

I am currently trying to update my datagridview via button click, add a user via text box and clicking a button i want the datagridview to update to reflect the current stat of the database. I have the datagridview showing up on launch of the software, but when I click the add button and try to refresh it, the database does not show.

Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Data
Add-Type -AssemblyName System.Collections

$jsonDB = Get-Content 'C:\Support\HardwareCollection.json' | Out-String | ConvertFrom-Json
#JsonDb has $JsonDB.update and $JsonDB.Date
$tableData = New-Object System.Collections.ArrayList
$tableData.AddRange($jsonDB)

$Form = New-Object System.Windows.Forms.Form 
$Form.Size = New-Object System.Drawing.Size(1050, 425) 
$Form.MaximizeBox = $False 
$Form.StartPosition = "CenterScreen" 
$Form.FormBorderStyle = 'Fixed3D' 
$Form.Text = "Hardware Collection"

$AddClientNButton = new-object System.Windows.Forms.Button
$AddClientNButton.Location = new-object system.drawing.size(61,90) 
$AddClientNButton.Size = new-object system.drawing.size(80,50)
$AddClientNButton.Text = "Add Client"
$AddClientNButton.Add_Click({AddClient}) 
$AddClientNButton.TabIndex = 10
$Form.Controls.Add($AddClientNButton)

$UserNametextBox = New-Object System.Windows.Forms.TextBox
$UserNametextBox.Location = New-Object System.Drawing.Point(1,1)
$UserNametextBox.Size = New-Object System.Drawing.Size(300,20)
$UserNametextBox.text="User Name"
$UserNametextBox.MaxLength = 6
$UserNametextBox.Add_Click({$this.SelectAll(); $this.Focus()})
$UserNametextBox.TabIndex = 0
$form.Controls.Add($UserNametextBox)

$dataGridView = New-Object System.Windows.Forms.DataGridView -Property @{
    Size = New-Object System.Drawing.Size(500, 200)
    Location = New-Object System.Drawing.Size(1, 150)
    ColumnHeadersVisible = $True
    DataSource = $tableData
    AutoSizeColumnsMode = 'AllCells'
    ColumnHeadersHeightSizeMode = 'AutoSize'
}


function AddClient
{
    $jsonDB = Get-Content 'C:\Support\HardwareCollection.json' | Out-String | ConvertFrom-Json
    $json.username

    $Date = Get-Date -Format "MM/dd/yyyy HH:mm:ss K" 
    $Username = $UserNametextBox.text

    if($jsonDB.username -eq $null)
        {
            $NewEntryItems=$Usernames
        }
    else
        {
            if($jsonDB.username -contains $Username)
            {
                $NewEntryItems =$null
            }
            else
            {
                $NewEntryItems = $username
            }
        }
    $CollectionData =  ForEach ($Username in $NewEntryItems)
    {
        New-Object PSObject -Property @{
            Username = $Username
            Date = $Date
        }
    }

    $jsonDB += $CollectionData

    $jsonDB | ConvertTo-Json -Compress  | 
    Set-Content C:\Support\HardwareCollection.json
    
    #refresh datagridview
    $dataGridView.DataBindings.DefaultDataSourceUpdateMode = 0
    $jsonDB = Get-Content 'C:\Support\HardwareCollection.json' | Out-String | ConvertFrom-Json
    #$dataGridView.DataSource = $jsonDB
    $tableData = New-Object System.Collections.ArrayList
    $tableData.AddRange($jsonDB)
    $dataGridView = New-Object System.Windows.Forms.DataGridView -Property @{
        Size = New-Object System.Drawing.Size(500, 200)
        Location = New-Object System.Drawing.Size(1, 150)
        ColumnHeadersVisible = $True
        DataSource = $tableData
        AutoSizeColumnsMode = 'AllCells'
        ColumnHeadersHeightSizeMode = 'AutoSize'
    }
}

$Form.Controls.Add($dataGridView)  
$Form.ShowDialog()

Any help would be amazing!!