code: public function group($id, array $children)
          {
              $parameters = [
              'query' => [],
              'body' => json_encode(['children' => $children], JSON_UNESCAPED_UNICODE),
              'headers' => [],
          ];
  
              $result = $this->post('v1/media/' . $id . '/group', $parameters);
  
              return $result;
          }
docs: Groups one "main" Media with one or more "child" Media.
  
  The main medium will by default be the only medium shown when searching, child media can be fetched by issuing a search with parentId set to the main medium id.
  
  @param int   $id       the Media identifier
  @param int[] $children an array of int values