Help with filtering products by brand in a Sanity.io structure

S.list()
      .title('/product')
      .items([
        S.documentTypeListItem('product').title('All products').icon(AllIcon),
        S.listItem()
          .title('Products by brand')
          .child(
            // List out all brands
            S.documentTypeList('brand')
              .title('Products by brand')
              .child((brandId) => S.documentList()
                .schemaType('product')
                .title('Products')
                .filter(
                  '_type == "product" && $brandId in brands[]._ref'
                )
                .params({ brandId }))
          )
      ])