uncaught in promises in vanilla js

I am making some mapping with moviedb api using innerhtml, the problem i am having is with the Main.appendChild where the appendChild is handle as a property and not as a function. I am having the same issue in the console with the entire main array and i think it might having something to do with the fact that i am declering the main object to a htmlelemnt then to a array. Btw i have given up on this project hence it wasnt worth the extra time that it took this is kinda of a filler part so excuse me pls.

const API_KEY = "api_key=0a2c754df24f03f4197199045aedf7de";
const BASE_URL = "https://api.themoviedb.org/3";
const API_URL = BASE_URL + "/discover/movie?sort_by=popularity.desc&" + API_KEY;
const IMG_URL = "https://image.tmdb.org/t/p/w500";

const main = document.getElementById("main");
getMovies(API_URL);

function getMovies(url) {
  fetch(url).then(res => res.json())
    .then(data => {
      console.log(data.results);
      showMovies(data.results);
    })
}

function showMovies(data) {
  main.innerHTML = " ";

  data.forEach(main => {
    const { title, vote_average, overview, poster_path } = main;

    const movieEl = document.createElement("div");
    movieEl.classList.add("movie");
    movieEl.innerHTML = `
  
                <img
                  src="${IMG_URL + poster_path} alt-""${title}"
                />
              </a>
            </div>
            <div class="list-content">
              <h2>
                <a href="single-movie.html" class="text-black"
                  ></a
                >
              </h2>
              <span class="list-meta">
                <span class="list-meta-item"
                  ><i class="fas fa-clock"></i> 2018</span
                >
                <a href="#" class="list-meta-item"
                  ><i class="fas fa-star"></i> ${vote_average}</a
                >
              </span>
              <p>
                ${overview}
              </p>
            </div>
          
    `;
    main.appendChild(movieEl);
  });
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta
name="viewport"
content="width=device-width, initial-scale=1, shrink-to-fit=no"
/>
<meta name="description" content="" />
<meta name="author" content="" />
<link rel="icon" href="img/favicon.png" />
<title>Movies - Get Booked Online</title>
<link rel="stylesheet" href="css/main.css" type="text/css" />
<link
href="https://fonts.googleapis.com/css?family=Roboto"
rel="stylesheet"
/>
<link
rel="stylesheet"
href="https://use.fontawesome.com/releases/v5.0.13/css/all.css"
integrity="sha384-DNOHZ68U8hZfKXOrtjWvjxusGo9WQnrNx2sqG0tfsghAvtVlRW3tvkXWZh58N9jp"
crossorigin="anonymous"
/>
<!-- Bootstrap core CSS -->
<link
rel="stylesheet"
href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css"
integrity="sha384-9gVQ4dYFwwWSjIDZnLEWnxCjeSWFphJiwGPXr1jddIhOegiu1FwO5qRGvFXOdJZ4"
crossorigin="anonymous"
/>
</head>
<body>
<nav class="navbar navbar-expand-md">
<a class="navbar-brand" href="index.html"><img src="img/logo.png" /></a>
<button
class="navbar-toggler"
type="button"
data-toggle="collapse"
data-target="#navbarsExampleDefault"
aria-controls="navbarsExampleDefault"
aria-expanded="false"
aria-label="Toggle navigation"
>
<i class="fas fa-bars"></i>
</button>
<div class="collapse navbar-collapse" id="navbarsExampleDefault">
<ul class="navbar-nav mr-auto">
<li class="nav-item">
<a class="nav-link" href="index.html"
><i class="fas fa-home"></i> Home</a
>
</li>
<li class="nav-item active">
<a class="nav-link" href="#"><i class="fas fa-film"></i> Movies</a>
</li>
</li>
<li class="nav-item dropdown">
<a
class="nav-link dropdown-toggle"
data-toggle="dropdown"
href="#"
role="button"
aria-haspopup="true"
aria-expanded="false"
><i class="fas fa-crown"></i> Genre</a
>
<div class="dropdown-menu">
<a class="dropdown-item" href="#">Adventure</a>
<a class="dropdown-item" href="#">Horror</a>
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Animation</a>
<a class="dropdown-item" href="#">Comedy</a>
<a class="dropdown-item" href="#">Fantasy</a>
</div>
</li>
</ul>
<a class="nav-button" href="movies.html"
><i class="fas fa-newspaper"></i> Latest Movies</a
>
</div>
</nav>
<!-- breadcrumbs -->
<nav aria-label="breadcrumb">
<ol class="breadcrumb">
<li class="breadcrumb-item"><a href="#">Home</a></li>
<li class="breadcrumb-item active" aria-current="page">Movies</li>
</ol>
</nav>
<!-- /breadcrumbs -->
<!-- movie cards -->
<div class="container">
<div class="alert alert-primary" role="alert">
<i class="fas fa-exclamation-circle"></i> The following movies are
currently in theaters.
</div>
<main id ="main">
<div class="row">
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/wCvTSaIQEweNdsU98usvt9re7fq.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black"
>Avengers: Infinity War</a
>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 8.8</a
>
</span>
<p>
As the Avengers and their allies have continued to protect the
world from threats too large for any one hero to handle, a new
danger has emerged from the cosmic shadows: Thanos.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/to0spRl1CMDvyUbOnbb4fTk3VAd.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black">Deadpool 2</a>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 8.3</a
>
</span>
<p>
Wisecracking mercenary Deadpool battles the evil and powerful
Cable and other bad guys to save a boy's life.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/uxzzxijgPIY7slzFvMotPv8wjKA.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black">Black Panther</a>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 7.6</a
>
</span>
<p>
King T'Challa returns home from America to the reclusive,
technologically advanced African nation of Wakanda to serve as
his country's new leader. However, T'Challa soon finds that he
is challenged for the throne by factions within his own country
as well as without.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/jjPJ4s3DWZZvI4vw8Xfi4Vqa1Q8.jpg"
/>
</a>
</div>
<div class="list-content">
<h2><a href="#" class="text-black">Fifty Shades Freed</a></h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 4.4</a
>
</span>
<p>
A young Silicon Valley tech-titan enlists a veteran surgeon with
a controversial past in starting a hospital with a cutting-edge,
new school approach to medicine.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/vLCogyfQGxVLDC1gqUdNAIkc29L.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black">Red Sparrow</a>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="single-movie.html" class="list-meta-item"
><i class="fas fa-star"></i> 6.7</a
>
</span>
<p>
Prima ballerina, Dominika Egorova faces a bleak and uncertain
future after she suffers an injury that ends her career. She
soon turns to Sparrow School, a secret intelligence service that
trains exceptional young people to use their minds and bodies as
weapons.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/30oXQKwibh0uANGMs0Sytw3uN22.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black">Rampage</a>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 6.4</a
>
</span>
<p>
Primatologist Davis Okoye shares an unshakable bond with George,
the extraordinarily intelligent, silverback gorilla who has been
in his care since birth. But a rogue genetic experiment gone
awry mutates this gentle ape into a raging creature of enormous
size.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/pU1ULUq8D3iRxl1fdX2lZIzdHuI.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black"
>Ready Player One</a
>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 8.8</a
>
</span>
<p>
When the creator of a popular video game system dies, a virtual
contest is created to compete for his fortune.
</p>
</div>
</div>
</div>
<div class="col-sm-6 col-xs-6">
<div class="list mb-2">
<div class="list-header">
<a href="single-movie.html" class="list-header-image">
<img
src="https://image.tmdb.org/t/p/w600_and_h900_bestv2/85R8LMyn9f2Lev2YPBF8Nughrkv.jpg"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black">Game Night</a>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> 6.2</a
>
</span>
<p>
Max and Annie's weekly game night gets kicked up a notch when
Max's brother Brooks arranges a murder mystery party -- complete
with fake thugs and federal agents. So when Brooks gets
kidnapped, it's all supposed to be part of the game.
</p>
</div>
</div>
</div>
</div>
</div>
</main>
<!-- /movie cards -->
<br />
<!-- Newsletter -->
<!-- /Newsletter -->
<!-- Footer -->
<footer class="footer">
<div class="container">
<div class="row">
<div class="col-lg-6 h-100 text-center text-lg-left my-auto">
<ul class="list-inline mb-2">
<li class="list-inline-item">
<a href="page.html">About us</a>
</li>
<li class="list-inline-item">&sdot;</li>
<li class="list-inline-item">
<a href="page.html">Refunds</a>
</li>
<li class="list-inline-item">&sdot;</li>
<li class="list-inline-item">
<a href="page.html">Terms and Privacy</a>
</li>
<li class="list-inline-item">&sdot;</li>
<li class="list-inline-item">
<a href="contact.html">Contact</a>
</li>
</ul>
<p class="small mb-4 mb-lg-0">
Omar Ahmad&copy; 2018. All Rights Reserved.
</p>
</div>
<div class="col-lg-6 h-100 text-center text-lg-right my-auto">
<ul class="list-inline mb-0">
<li class="list-inline-item mr-3">
<a href="https://linkedin.com/in/byalk" class="footer-fb">
<i class="fab fa-linkedin fa-2x fa-fw"></i>
</a>
</li>
<li class="list-inline-item mr-3">
<a href="#" class="footer-tw">
<i class="fab fa-twitter fa-2x fa-fw"></i>
</a>
</li>
<li class="list-inline-item">
<a href="#" class="footer-in">
<i class="fab fa-instagram fa-2x fa-fw"></i>
</a>
</li>
</ul>
</div>
</div>
</div>
</footer>
<!-- /Footer -->
<!-- Bootstrap core JavaScript
================================================== -->
<!-- Placed at the end of the document so the pages load faster -->
<script
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crossorigin="anonymous"
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></script>
<script src="script.js"></script>
</body>
</html>

Answer

You have two variables named ‘main’, one is the getElementById and the other is from the forEach loop. Change one and it should work

const BASE_URL = "https://api.themoviedb.org/3";
const API_URL = BASE_URL + "/discover/movie?sort_by=popularity.desc&" + API_KEY;
const IMG_URL = "https://image.tmdb.org/t/p/w500";
const mainEl = document.getElementById("main");
getMovies(API_URL);
function getMovies(url) {
fetch(url)
.then((res) => res.json())
.then((data) => {
console.log(data.results);
showMovies(data.results);
});
}
function showMovies(data) {
main.innerHTML = " ";
data.forEach((main) => {
const { title, vote_average, overview, poster_path } = main;
const movieEl = document.createElement("div");
movieEl.classList.add("movie");
movieEl.innerHTML = `
<img
src="${IMG_URL + poster_path} alt-""${title}"
/>
</a>
</div>
<div class="list-content">
<h2>
<a href="single-movie.html" class="text-black"
></a
>
</h2>
<span class="list-meta">
<span class="list-meta-item"
><i class="fas fa-clock"></i> 2018</span
>
<a href="#" class="list-meta-item"
><i class="fas fa-star"></i> ${vote_average}</a
>
</span>
<p>
${overview}
</p>
</div>
`;
mainEl.appendChild(movieEl);
});
}

Sandbox Code