Getting strange artifacts in URL from Flask's url_for

I can’t seem to find anything on this particular problem. I’m using the url_for in an html page and it’s returning some funky stuff right before the query string. What’s causing the below behavior and how can I get the actual URL to match what’s expected?

The call: href="{{ url_for('add_movie', tmdb_id=movie['movie_id']) }}"

Expected URL: ‘/add?tmdb_id=1234’

Actual URL: ‘/add/%7Btmdb_id%7D?tmdb_id=1234′ (the strange part in bold)

The list of movies is populated from a function that makes an API call. I verified that the list of id‘s returned from the API call looks good.

Python:

class TmdbMovie:
    def __init__(self, tmdb_id, title, release_date):
        self.movie_id = tmdb_id
        self.title = title
        self.release_date = release_date

@app.route('/add/{tmdb_id}', methods=['POST'])
def add_movie(tmdb_id):

HTML:

{% for movie in movies %}
  <p>
    <a href="{{ url_for('add_movie', tmdb_id=movie['movie_id']) }}"> {{ movie['title'] }} - {{ movie['release_date'] }}</a>
  </p>
{% endfor %}