I'm trying to get the backdrops for the film "Shooting war" (5707) but the API returns an empty element for backdrops... any clue?

API Call to get backdrops:

https://api.themoviedb.org/3/movie/tt0298506/images?api_key=<valid_key>

Response:

{
  "id": 41327,
  "backdrops": [],
  "posters": [
    {
      "aspect_ratio": 0.73,
      "file_path": "/aCAg25GJ46o489DTzB6HfEefxj2.jpg",
      "height": 907,
      "iso_639_1": null,
      "vote_average": 0.0,
      "vote_count": 0,
      "width": 666
    }
  ]
}

Thanks in advance!