Sonata\Component\Payment\TransactionInterface::setTransactionId PHP Method

    public function setTransactionId($transactionId);

 /**
  * return the transaction_id sent by the bank
  *
  * @param  TransactionInterface $transaction
  * @return void
  */
 public function applyTransactionId(TransactionInterface $transaction)
 {
     $transactionId = $transaction->get('txn_id', null);
     if (!$transactionId) {
         // no transaction id provided
         $transactionId = -1;
     }
     $transaction->setTransactionId($transactionId);
 }