In the API doumentation https://developer.themoviedb.org/reference/movie-details the response description shows field 'belongs_to_collection' as a string, yet when actually running a request that field is shown as an object:

  "belongs_to_collection": {
    "id": 264,
    "name": "Back to the Future Collection",
    "poster_path": "/5Xsu2o5IsZRuuxCEVZ9nVve21FP.jpg",
    "backdrop_path": "/AqQotqj7XOI6GjB28nhMMa8YzOT.jpg"
  },

So there seems to be a flaw in the documentation.

Kind Regards, Gerd Rother