code: public function retrieveFileData($id, $template = null, CachePolicy $cachePolicy = null)
          {
              $parameters = [
              'query' => ['template' => $template],
              'body' => json_encode([]),
              'headers' => [],
          ];
  
              $result = $this->get('v1/media/' . $id . '/asset', $parameters, $cachePolicy);
  
              return $result;
          }
docs: Gets the raw file data of a Media.
  
  You may append an optional template parameter to the query. Omitting the template parameter will return the medium thumbnail.
  
  Existing templates are:
  <b>original</b> - The original file
  <b>preview</b> - A preview image, sized 1000px on the long side
  <b>thumb_small</b> - A thumbnail image, sized 100px on the long side
  <b>thumb_medium</b> - A thumbnail image, sized 200px on the long side
  <b>thumb_large</b> - A thumbnail image, sized 300px on the long side
  <b>videopreview</b> - A preview video, sized 360p and maximum 2min
  <b>{integer}</b> - An image template identifier (NOTE: You can only request templates that are available on the server, eg. a media that have been published using COPY or SYMLINK-protocols)
  
  @param int         $id          The Media identifier..
  @param string      $template    Optional template of Media..
  @param CachePolicy $cachePolicy a custom cache policy used for this request only
  
  @return string The raw file data