What is bad in this code?

Code - what is bad here.cs

using System;
using System.IO;
using System.Net;
using System.Net.Mail;

namespace Interview;

public class WhatIsBadHere
{
	private static readonly string _connectionString = "Server=localhost;Database=MyLocalDb;Trusted_Connection=True";

	public void ProcessOrder(string custEmail, decimal amt)
	{
		try {
			if (amt > 1000) {
				Console.WriteLine($"Discount applied for customer '{custEmail}'!");
				amt *= 0.95m;
			}

			FileStream fs = new FileStream("order.txt", FileMode.Create);
			StreamWriter sw = new StreamWriter(fs);

			if (custEmail != null && !string.IsNullOrEmpty(custEmail)) {
				if (amt > 0) {
					var db = new Database()
					db.SaveOrder(custEmail, amt);

					try {
						var emailService = new EmailService();
						emailService.SendEmail(custEmail, "Thank you for your order. It is being processed!");
					}
					catch (Exception ex) {
					}

					sw.Write($"Customer: {custEmail}, Amount: {amt:C}");
				}
			}
		}
		catch (Exception ex) {
			Console.WriteLine(ex.ToString());
		}
	}
}

public class Database
{
	public static void SaveOrder(string custEmail, decimal amount)
	{
		using (var conn = new SqlConnection(_connectionString)) {
			conn.OpenAsync();
			var cmd = new SqlCommand($"INSERT INTO Orders VALUES ('{custEmail}', {amount})", conn);
			cmd.ExecuteNonQueryAsync();
		}
	}
}

public static class EmailService
{
	public static void SendEmail(string email, string message)
	{
		SmtpClient client = new SmtpClient("smtp.example.com") {
			Credentials = new NetworkCredential("some-user", "some-password")
		};

		client.SendMailAsync("[email protected]", email, "Orders", message);
	}
}