code: public function onInsert(ResourceEventInterface $event)
      {
          $payment = $this->getPaymentFromEvent($event);
  
          // Generate number and key
          $changed = $this->generateNumber($payment);
          $changed |= $this->generateKey($payment);
  
          // Exchange rate
          $changed |= $this->updateExchangeRate($payment);
  
          // Completed state
          $changed |= $this->handleCompletedState($payment);
  
          if ($changed) {
              $this->persistenceHelper->persistAndRecompute($payment);
          }
  
          $sale = $this->getSaleFromPayment($payment);
  
          $this->customerUpdater->handlePaymentInsert($payment);
  
          $this->scheduleSaleContentChangeEvent($sale);
      }
docs: Insert event handler.
  
  @param ResourceEventInterface $event