public ActionResult <SignedTransactionResponse> SignAsync(
            [FromBody] SignTransactionRequest signRequest)
        {
            var signedTransaction = _signService.SignTransaction
                                    (
                transactionContext: signRequest.TransactionContext,
                privateKey: signRequest.PrivateKeys[0]
                                    );

            return(new SignedTransactionResponse
            {
                SignedTransaction = signedTransaction
            });
        }