In this blog you will see how to resolve “Convert-SPWebApplication : A positional parameter cannot be found that accepts argument '['.“ issue in PowerShell.
I was working on the migration from SharePoint 2010 to SharePoint 2013. I was trying to convert SharePoint 2010 classic-mode web application to a SharePoint 2013 claims-based authentication using “Convert-SPWebApplication” cmdlet as shown below in PowerShell. I was getting the following Error.
Convert-SPWebApplication -Identity "https://<webappurl>" -To Claims -RetainPermissions [-Force]
Remove the square brackets for Force parameter. Square brackets just signify that the parameter is optional.