Error: The RSS file isn’t working

We tried to get the RSS file for this podcast - https://feeds.viertausendhertz.de/elementarfragen - but it wouldn’t load for us.

array (
  'wrapperType' => 'track',
  'kind' => 'podcast',
  'artistId' => 1079021194,
  'collectionId' => 1076864574,
  'trackId' => 1076864574,
  'artistName' => 'Viertausendhertz',
  'collectionName' => 'Elementarfragen',
  'trackName' => 'Elementarfragen',
  'collectionCensoredName' => 'Elementarfragen',
  'trackCensoredName' => 'Elementarfragen',
  'artistViewUrl' => 'https://podcasts.apple.com/us/artist/viertausendhertz/1079021194?uo=4',
  'collectionViewUrl' => 'https://podcasts.apple.com/us/podcast/elementarfragen/id1076864574?uo=4',
  'feedUrl' => 'https://feeds.viertausendhertz.de/elementarfragen',
  'trackViewUrl' => 'https://podcasts.apple.com/us/podcast/elementarfragen/id1076864574?uo=4',
  'artworkUrl30' => 'https://is3-ssl.mzstatic.com/image/thumb/Podcasts113/v4/c0/ef/33/c0ef33df-c401-15f4-4f79-54da61a46342/mza_8072372109828877548.jpg/30x30bb.jpg',
  'artworkUrl60' => 'https://is3-ssl.mzstatic.com/image/thumb/Podcasts113/v4/c0/ef/33/c0ef33df-c401-15f4-4f79-54da61a46342/mza_8072372109828877548.jpg/60x60bb.jpg',
  'artworkUrl100' => 'https://is3-ssl.mzstatic.com/image/thumb/Podcasts113/v4/c0/ef/33/c0ef33df-c401-15f4-4f79-54da61a46342/mza_8072372109828877548.jpg/100x100bb.jpg',
  'collectionPrice' => 0.0,
  'trackPrice' => 0.0,
  'trackRentalPrice' => 0,
  'collectionHdPrice' => 0,
  'trackHdPrice' => 0,
  'trackHdRentalPrice' => 0,
  'releaseDate' => '2019-11-01T10:00:00Z',
  'collectionExplicitness' => 'cleaned',
  'trackExplicitness' => 'cleaned',
  'trackCount' => 27,
  'country' => 'USA',
  'currency' => 'USD',
  'primaryGenreName' => 'Society & Culture',
  'contentAdvisoryRating' => 'Clean',
  'artworkUrl600' => 'https://is3-ssl.mzstatic.com/image/thumb/Podcasts113/v4/c0/ef/33/c0ef33df-c401-15f4-4f79-54da61a46342/mza_8072372109828877548.jpg/600x600bb.jpg',
  'genreIds' => 
  array (
    0 => '1324',
    1 => '26',
    2 => '1533',
    3 => '1535',
  ),
  'genres' => 
  array (
    0 => 'Society & Culture',
    1 => 'Podcasts',
    2 => 'Science',
    3 => 'Social Sciences',
  ),
)...https://itunes.apple.com/lookup?id=1076864574

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