code: private function getDownlineSnapshot($dateOn)
      {
          /* collect downline data to given date */
          $query = $this->qbSnapOnDate->build();
          $conn = $query->getConnection();
          $bind = [$this->qbSnapOnDate::BND_ON_DATE => $dateOn];
          $result = $conn->fetchAll($query, $bind);
          return $result;
      }
docs: Get Downline Tree snapshot on the $datestamp. Result is an array [$customerId => [...], ...]
  
  @param $dateOn 'YYYYMMDD'
  
  @return array|null