private function createOperation($accIdDebit, $accIdCredit, $amount, $note)
    {
        /* prepare transaction */
        $tran = new ETrans();
        $tran->setDebitAccId($accIdDebit);
        $tran->setCreditAccId($accIdCredit);
        $tran->setValue($amount);
        $tran->setNote($note);
        /* perform operation */
        $req = new \Praxigento\Accounting\Api\Service\Operation\Create\Request();
        $req->setOperationTypeCode(Cfg::CODE_TYPE_OPER_WALLET_REFUND);
        $req->setTransactions([$tran]);
        $req->setOperationNote($note);
        $resp = $this->servOper->exec($req);
        $result = $resp->getOperationId();
        return $result;
    }