code: public function requestAccess($when, $duration, array $visitors, $phoneNumber)
      {
          return $this->call(self::SERVICE, 'requestAccess', [$when, $duration, $visitors, $phoneNumber]);
      }
docs: Request access to the data-center.
  
  @param string   $when        Datetime of the wanted data-center access, in YYYY-MM-DD hh:mm:ss format
  @param int      $duration    Expected duration of the visit, in minutes
  @param string[] $visitors    Names of the visitors for this data-center visit, max amount of visitors is 20
  @param string   $phoneNumber Phone number to receive access codes on
  
  @throws \SoapFault
  
  @return \TransIP\Model\DataCenterVisitor[]