public async Task <ResponseDto> MakePayment(PaymentRequestDto dto)
        {
            var result = new ResponseDto();

            //validation of request data
            var paymentProvider = _context.PaymentProviders
                                  .SingleOrDefault(x => x.PaymentProviderUniqueToken == dto.PaymentProviderUniqueToken);

            if (paymentProvider is null)
            {
                result.Status     = PaymentStatus.Failed;
                result.ResultCode = ResultCode.PaymentProviderError;
                return(result);
            }

            var card = _context.Cards
                       .SingleOrDefault(x =>
                                        string.Format("{0} {1}", x.Client.FirstName, x.Client.LastName) == dto.CardHolderName &&
                                        x.CardNumber == x.CardNumber &&
                                        x.ExpirationDate == x.ExpirationDate &&
                                        x.Cvc == x.Cvc);

            if (card is null)
            {
                result.Status     = PaymentStatus.Failed;
                result.ResultCode = ResultCode.CardError;
                return(result);
            }
            else if (card.Balance < dto.Amount)
            {
                result.Status     = PaymentStatus.Failed;
                result.ResultCode = ResultCode.CardBalanceError;
                return(result);
            }
            card.Balance -= dto.Amount;

            //create and save new transaction in db
            var transaction = new Transaction
            {
                PaymentProvider      = dto.PaymentProviderUniqueToken,
                TimeStamp            = dto.TimeStamp,
                Amount               = dto.Amount,
                PaymentProviderToken = dto.PaymentProviderUniqueToken,
                CardId               = card.Id,
                Status               = result.Status,
                ResultCode           = result.ResultCode
            };

            _context.Transactions.Add(transaction);
            //update card data and save all changes in db
            await _context.MockSaveChangesAsync();

            //if all request data is valid, take paymeny amount from card's balance
            result.Status      = PaymentStatus.Paid;
            result.ResultCode  = ResultCode.Success;
            result.OperationId = Guid.NewGuid();//Mock transactionId

            return(result);
        }