URLRepresentableEntity with custom properties

I am trying to implement URLRepresentableEntity on my AppEntity

I am following along with the WWDC video here

All compiles fine when I use the ID as in the video:

extension SceneEntity: URLRepresentableEntity {
  static var urlRepresentation: URLRepresentation {
    "https://example.com/scene/\(.id)"
  }
}

but my URLs need to use a different property on the Entity. The WWDC video clearly states: "Notice that I'm using the entity’s identifier as an interpolated value. You can use an entity’s ID or any of its properties with the @Property attribute as interpolations in the URL string."

So I annotated my entity with the @Property attribute and expected that to work but it doesn't compile.

struct SceneEntity: AppEntity {
  let id: UUID
  @Property(title: "Slug") var slug: String
}


extension SceneEntity: URLRepresentableEntity {
  static var urlRepresentation: URLRepresentation {
    "https://example.com/scene/\(.slug)"
  }
}

Type 'EntityURLRepresentation<SceneEntity>.StringInterpolation.Token' has no member 'slug'

How can I use this API with a property that is not the ID?