This a set of Python scripts that scrapes a Letterboxd watchlist and then adds the movies from that list to your Plex watchlist. If a movie is not available in your Plex library, the missing movies will then be added to your Radarr instance.
If the PLEX_TOKEN or PLEX_HOST variables are not applied, all movies on the watchlist will attempt to be added to Radarr. The script can also be used without Radarr.
https://support.plex.tv/articles/204059436-finding-an-authentication-token-x-plex-token/
Your API key can be found in Settings > General in the Radarr Web UI.
docker run --rm \
-e LETTERBOXD_USERNAME='{Letterboxd username}' \
-e PLEX_TOKEN='{Plex token}' \
-e PLEX_HOST='http://{Plex server's IP}:32400' \
-e RADARR_TOKEN='{radarr api key}' \
-e RADARR_HOST='http://{Radarr instance IP}:7878' \
choff3/letterboxd-sync
Thanks to L-Dot for the Letterboxd list scraper. https://github.com/L-Dot/Letterboxd-list-scraper