New-UDApp error

Product: PowerShell Universal
Version: 4.2.12

I am new to PSU. When I tried some of the tutorial with New-UDApp, it is giving a ‘Theme’ error.

Here is the code I tested:
New-UDApp -Title “Hello, World!” -Content {
New-UDButton -Text “Click Me” -OnClick {
Show-UDToast -Message ‘Success!!’

Here is the error I got:
New-UDApp : Cannot process argument transformation on parameter ‘Theme’. Cannot convert the “System.Object” value of type “System.Object” to type “System.Collections.Hashtable”.

What am I doing wrong here?