private async void MakePaymentButton_Click(object sender, EventArgs e)
 {
     employee = employees[EmployeesBox.SelectedIndex];
     if (ValidatePaymenForm())
     {
         PaymentModel payment = new PaymentModel()
         {
             PaymentAmount = CalculatePayment(employee),
             PaymentDate   = DateTime.Now,
             EmployeeId    = employee.Id
         };
         await payment.AddPayment();
     }
     else
     {
         MessageBox.Show("Проверьте правильность введенных данных", "Ошибка в заполнении формы",
                         MessageBoxButtons.OK, MessageBoxIcon.Error);
     }
 }