private async Task <string> FetchSigningKeyAsync(string vaspSmartContractAddress)
        {
            var vaspContract    = new VASPContractService(_web3, vaspSmartContractAddress);
            var signingKeyBytes = await vaspContract.SigningKeyQueryAsync();

            return(signingKeyBytes.ToHex());
        }
        private async Task <string> FetchMessageKeyAsync(string vaspSmartContractAddress)
        {
            var vaspContract      = new VASPContractService(_web3, vaspSmartContractAddress);
            var transportKeyBytes = await vaspContract.MessageKeyQueryAsync();

            return(transportKeyBytes.ToHex());
        }