I have alertview with textfield for otp validation,but if OTP is mismatched then alertView will not be dismissed

Question

I have alertview with textfield for otp validation,but if OTP is mismatched then another alertView will show message "OTP not matched", and on click ok button then previous alertview (alertview with OTP textfield) will appeared again to enter OTP.

@IBAction func btnRegisterTapped(_ sender: UIButton) {
  if !Validate(){
    return
  }
  // get otp session
  APIController.registerUser(Email:  self.txtfldEmail.text!, Nonce: self.registerNonce) { (data1) in
    print("data1 :=> \(data1)")

    let alertController = UIAlertController(title: "BrainCal", message: "Please verify your OTP for login", preferredStyle: .alert)

    let OkAction = UIAlertAction(title: "OK", style: .default, handler: {
      alert -> Void in

      APIController.registerUserWithOtp(Email: self.txtfldEmail.text!, Password: "", Nonce: self.registerNonce, Otp: (alertController.textFields?.first?.text!)!, Otp_Session: "\(data1["otp_session"]!)", SuccessHandler: { (response) in
        print(response)
        let dict = response as NSDictionary

        if  UserDefaults.standard.value(forKey: "LoginUserData") != nil{
          UserDefaults.standard.removeObject(forKey: "LoginUserData")
        }
        UserDefaults.standard.set(NSKeyedArchiver.archivedData(withRootObject: dict), forKey: "LoginUserData")

        self.performSegue(withIdentifier: "MainSegue", sender: self)
      })
    })
    alertController.addTextField { (textField : UITextField!) -> Void in
      textField.placeholder = "Enter Otp Here"
      textField.keyboardType = .numberPad

      NotificationCenter.default.addObserver(forName: NSNotification.Name.UITextFieldTextDidChange, object: textField, queue: OperationQueue.main) { (notification) in
        OkAction.isEnabled = textField.text!.characters.count > 0
      }
    }
    OkAction.isEnabled = false
    alertController.addAction(OkAction)
    self.present(alertController, animated: true, completion: nil)
  }
}