How to fetch metadata (e.g., rss, episodes...) of podcasts by Apple Podcasts ids (iTunes ids) or Spotify ids?
Use POST /podcasts with the "itunes_ids" or "spotify_ids" parameter to fetch up to 10 podcasts at once.

If you pass the "show_latest_episode=1" parameter to POST /podcasts, you'll get latest episodes of those podcasts, which is useful to check new episodes of subscribed podcasts.
If you haven't used Listen Notes Podcast API yet, get API keys here - Get API keys