New Post: installTitle not working in StatusMessage?

Show-InstallationProgress -StatusMessage 'Uninstalling application [$installTitle]. Please Wait...'

above line should had shown me thi

Variables: Application

[string]$appVendor = 'Igor Pavlov'
[string]$appName = '7-Zip'
[string]$appVersion = '9.35 beta'

[string]$installTitle = "$appVendor $appName $appVersion"

but i getting the this:

'Uninstalling application [$installTitle]. Please Wait...'

What wrong with the string since it doesnt show this:

'Uninstalling application Igor Parlov 7-Zip 9.35 Beta. Please Wait...'