add gmail annotation image

Question

I suggest to use Gmail Annotations, its type is "PromotionCard" as in documentation https://developers.google.com/gmail/promotab/overview?hl=ru

{
  "@context": "http://schema.org/",
  "@type": "PromotionCard",
  "image": "...",
  "url":"..."
}

but when trying to validate in https://validator.schema.org/, it writes an error about an unknown type