XML : Editing an XML object - IdentityProvider [duplicate]

This question already has an answer here:

• Editing an XML object - Connection Strings 1 answer

I am attempting to alter a value of an XML object with another value. However my reassignment is failing with an error:

A positional parameter cannot be found that accepts argument '='

  $webConfig.configuration.Configuration.SingleSignOnConfiguration.IdentityProviders.add |    ? {$_.name -eq "IdentityProvider"} |    select Name = $identityProviderName    

Can someone correct my syntax and tell me why? Is it because the left side of the argument is not interpreted as a single value? I know my XML is fine as I use this code to pull the value I need.