code: public function typeAsString($plural = false)
      {
          $type = null;
          switch ($this->type) {
              case self::PLAN_ONETIME:
                  $type = 'application_charge';
                  break;
              default:
              case self::PLAN_RECURRING:
                  $type = 'recurring_application_charge';
                  break;
          }
  
          return $plural ? "{$type}s" : $type;
      }
docs: Returns the plan type as a string (for API).
  
  @param bool $plural Return the plural form or not.
  
  @return string