This example is taken from list add items page. The url should be "https://api.themoviedb.org/4/list/list_id/items" instead of "https://api.themoviedb.org/4/list_id/items".

const axios = require('axios');

const options = {
  method: 'POST',
  url: 'https://api.themoviedb.org/4/list_id/items',
  headers: {
    accept: 'application/json',
    'content-type': 'application/json',
    Authorization: 'Bearer eyJhbGciOiJIUzI1NiJ9.eyJhdWQiOiJhYTYzOWRkNWY0NmU1N2M5YTJkNDY5MzlkZGE1OTYxOSIsInN1YiI6IjY1NDYyNjM0NDFhNTYxMzM2ZDg0MzlhZiIsInNjb3BlcyI6WyJhcGlfcmVhZCJdLCJ2ZXJzaW9uIjoxfQ.2cdP4naZMke4IQDr_Lt4e86H6jDuZ8d0nGWq75OqdUk'
  },
  data: {
    items: [
      {media_type: 'movie', media_id: 550},
      {media_type: 'movie', media_id: 244786},
      {media_type: 'tv', media_id: 1396}
    ]
  }
};

axios
  .request(options)
  .then(function (response) {
    console.log(response.data);
  })
  .catch(function (error) {
    console.error(error);
  });