Import Xml and Csv files into database

I have a simple service class here which import csv or xml file into database using .NET Standard library C#.

Do you have any comments? Are there any recommended techniques to use instead of the switch statement in the method ProcessPaymentFile?

public class AbcPaymentService : IAbcPaymentService
{
    private readonly IAbcPaymentContext _abcPaymentContext;
    private readonly IConfiguration _configuration;
    public AbcPaymentService(IAbcPaymentContext abcPaymentContext, IConfiguration configuration)
    {
        _abcPaymentContext = abcPaymentContext;
        _configuration = configuration;
    }

    public List<PaymentTransactionDetailResponse> GetTransactionsByCurrency(string currency)
    {
        var paymentTransactions = _abcPaymentContext.PaymentTransactions.Where(p => p.CurrencyCode == currency).ToList();

        return MapPaymentTransactions(paymentTransactions);
    }

    public List<PaymentTransactionDetailResponse> GetTransactionsByDateRange(DateTime dateFrom, DateTime dateTo)
    {            
        var paymentTransactions = _abcPaymentContext.PaymentTransactions
            .Where(p => p.TransactionDate >= dateFrom && p.TransactionDate <= dateTo).ToList();

        return MapPaymentTransactions(paymentTransactions);
    }

    public List<PaymentTransactionDetailResponse> GetTransactionsByStatus(string status)
    {
        // add more validation. ie. check length. 

        var paymentTransactions = _abcPaymentContext.PaymentTransactions.Where(p => p.Status == status).ToList();

        return MapPaymentTransactions(paymentTransactions);
    }

    public void ProcessPaymentFile(IFormFile file)
    {
        #region Validation
        var fileExtension = Path.GetExtension(file.FileName);

        var validFileTypes = new[] { ".csv",".xml"}; // move to appsetting for easier configuration.            
        bool isValidType = validFileTypes.Any(t => t.Trim() == fileExtension.ToLower());

        if (isValidType == false)
            throw new ArgumentException($"Unknown format.");

        if(file.Length > 1000) // move to appsetting for easier configuration.
            throw new ArgumentException($"Invalid file size. Only less than 1 MB is allowed.");
        #endregion

        // Upload file to server
        var target = _configuration["UploadPath"];

        var filePath = Path.Combine(target, file.FileName);

        try
        {
            using (var stream = new FileStream(filePath, FileMode.Create))
            {
                file.CopyTo(stream);
            }

            switch (fileExtension.ToLower())
            {
                case ".csv":
                    var config = new CsvConfiguration(CultureInfo.InvariantCulture)
                    {
                        HasHeaderRecord = false,                            
                    };
                    using (var reader = new StreamReader(filePath)) {
                        using (var csv = new CsvReader(reader, config))
                        {
                            csv.Context.RegisterClassMap<CsvMap>();
                            var paymentTransactionCsv = csv.GetRecords<Models.Xml.Transaction>().ToList();

                            SaveToDb(paymentTransactionCsv);
                        }
                    }                        
                    break;
                case ".xml":
                    var serializer = new XmlSerializer(typeof(Models.Xml.Transactions));

                    using (TextReader reader = new StreamReader(new FileStream(filePath, FileMode.Open)))
                    {
                        var paymentTransactionXml = (Models.Xml.Transactions)serializer.Deserialize(reader);

                        SaveToDb(paymentTransactionXml.Transaction);
                    }
                    break;
                default:
                    throw new ArgumentException($"Invalid file type. Only {string.Join(",", validFileTypes)} allowed.");
            }
        }
        catch (Exception ex)
        {
            throw new Exception(ex.Message);
        }            
    }

    #region PrivateFunctions
    private void SaveToDb(List<Models.Xml.Transaction> paymentTransactions)
    {
        if (PaymentTransactionXmlIsValid(paymentTransactions) == false)
            throw new Exception("Invalid transaction."); // todo: write into log file or db

        // if all validation passed, map objects and 
        var paymentTransactionsEntity = paymentTransactions.Select(p => new PaymentTransaction()
        {
            TransactionId = p.Id,
            TransactionDate = p.TransactionDate,
            Amount = Convert.ToDecimal(p.PaymentDetails.Amount),
            CurrencyCode = p.PaymentDetails.CurrencyCode,
            Status = Mapper.MapStatus(p.Status)
        })
        .ToList();

        // save into db.
        _abcPaymentContext.PaymentTransactions.AddRange(paymentTransactionsEntity);
        _abcPaymentContext.SaveChanges();

        // todo: don't insert duplicate transaction
    }

    private bool PaymentTransactionXmlIsValid(List<Models.Xml.Transaction> paymentTransactions)
    {
        foreach (var trans in paymentTransactions)
        {
            if (string.IsNullOrEmpty(trans.Id)) return false;
            if (trans.TransactionDate == null) return false;
            if(trans.PaymentDetails.Amount == 0) return false;
            if (string.IsNullOrEmpty(trans.PaymentDetails.CurrencyCode)) return false;
            if (string.IsNullOrEmpty(trans.Status)) return false;             
        }
        return true;
    }

    private List<PaymentTransactionDetailResponse> MapPaymentTransactions(List<PaymentTransaction> paymentTransactions) {
        // Construct Dto responses model.
        var paymentTransactionDetailResponses = paymentTransactions.Select(p => new PaymentTransactionDetailResponse()
        {
            Id = p.TransactionId.ToString(),
            Payment = $"{p.Amount} {p.CurrencyCode}",
            Status = p.Status
        }).ToList();

        return paymentTransactionDetailResponses;
    }
    #endregion
}