Hi, I need help with Iframe preview, I have a `route` schema with unique `slug` (`/lb/123`) and also I have `page` schema with the content for that route now the problemis...

{
      name: 'page',
      type: 'reference',
      validation: (Rule) => Rule.required(),
      description: 'The page you want to appear at this path. Remember it needs to be published.',
      to: [
        {
          type: 'page'
        }
      ]
    },

 S.documentList()
              .title('Active pages')
              .id('pages')
              .schemaType('page')
              .menuItems(S.documentTypeList('page').getMenuItems())
              .filter('_type == "page" && _id in *[_type == "route"].page._ref')
              .child(async documentId => {
                const slug = await client.fetch(
                  `*[_type == "route" && page._ref == $documentId][0].slug.current`,
                  { documentId }
                )
                return S.document()
                  .documentId(documentId)
                  .schemaType('page')
                  .views([
                    S.view.form(),
                    S.view.component(PagePreview).title('preview'.options({ slug })
                  ])
              })
          ),

import client from 'part:@sanity/base/client