code: public function setPickupPoint($pickup_point_id)
      {
          $service = new AdditionalService();
          $service->setServiceCode(2106); // alternative pickup point
          $service->addSpecifier('pickup_point_id', $pickup_point_id);
  
          $this->addAdditionalService($service);
      }
docs: Sets a pickup point for the shipment.
  
  @param $pickup_point_id