curl --request GET \
  --url https://api.example.com/api/apps/beta/apps/{appId}/thumbnail/metadata \
  --header 'X-Domino-Api-Key: <api-key>'

{
  "contentType": "<string>",
  "etag": "<string>",
  "sizeBytes": 123,
  "updatedAt": 123,
  "filename": "<string>"
}