protected void payButton_OnServerClick(object sender, EventArgs e) { if (amountTextBox.Value.Trim().Length == 0 || dueDateTextBox.Value.Length == 0) { paymentLabel.Text = "Payment Information is not valid."; } else { Patient patient = (Patient)ViewState["Patient"]; double totalFee = patient.TotalFee; if (Convert.ToDouble(amountTextBox.Value) == totalFee) { paymentLabel.Text = billManager.UpdateBillInformation(patient.PhoneNumber); } else if (Convert.ToDouble(amountTextBox.Value) == 0) { paymentLabel.Text = "Bill is Unpaid."; } else { paymentLabel.Text = "Partial payment is not possible."; } } }