Error Message Swift 4.2

Hi guys.
Help me!
My API is perfect.

My code Swift is stranger error, but it writes perfectly to the database via API.

@IBAction func register_click(_ sender: Any) {
//if not text

    if usernameTxt.text!.isEmpty || passwordTxt.text!.isEmpty || emailTxt.text!.isEmpty || firstnameTxt.text!.isEmpty || lastnameTxt.text!.isEmpty {
        usernameTxt.attributedPlaceholder = NSAttributedString(string: "username", attributes: [NSAttributedStringKey.foregroundColor:])
        passwordTxt.attributedPlaceholder = NSAttributedString(string: "password", attributes: [NSAttributedStringKey.foregroundColor:])
        emailTxt.attributedPlaceholder = NSAttributedString(string: "email", attributes: [NSAttributedStringKey.foregroundColor:])
        firstnameTxt.attributedPlaceholder = NSAttributedString(string: "name", attributes: [NSAttributedStringKey.foregroundColor:])
        lastnameTxt.attributedPlaceholder = NSAttributedString(string: "surname", attributes: [NSAttributedStringKey.foregroundColor:])
    } else {
        // if entered - create new user mysql
        // remove keyboard
        // url to php file
        let url = URL(string: "http://localhost/Twiter/register.php")
        // request to php file
        var request = URLRequest(url: url!)
        // method to pass data to this file (e.g. via  POST)
        request.httpMethod = "POST"
        //request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
        //request.addValue("application/json", forHTTPHeaderField: "Accept")
        //request.setValue( "application/json", forHTTPHeaderField: "Authorization")
        //request.setValue("application/json; application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
        // body to be appended to url
        let body = "username=\(usernameTxt.text!.lowercased())&password=\(passwordTxt.text!)&email=\(emailTxt.text!)&fullname=\(firstnameTxt.text!)%20\(lastnameTxt.text!)"
        request.httpBody = .utf8) //allowLossyConversion: true
        // proceed request URLSession.shared.dataTask(with: request) { data, response, error in
        URLSession.shared.dataTask(with: request) { data, response, error in
            if error == nil {
                guard let data = data else {return}
                // get main queue in code process to communicate back to UI
                DispatchQueue.main.async(execute: {
                 do {
                 // get json result
                 let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? NSDictionary //.allowFragments
                 // assign json to new var parseJSON in guard/secured way
                    guard let parseJSON = json else {
                 print("Error parsing parsing")
                 // get id from parseJSON dictionary
                 let id = parseJSON["id"]
                 // successfully registered
                 if id != nil {
                 /*DispatchQueue.main.async(execute: {
                 let message = parseJSON["message"] as! String
                 appDelegate.infoView(message: message, color: colorLightGreen)
                 // save user information we received from our host
                 UserDefaults.standard.set(parseJSON, forKey: "parseJSON")
                 user = UserDefaults.standard.value(forKey: "parseJSON") as? NSDictionary
                 // go to tabbar / home page
                 DispatchQueue.main.async(execute: {
                 // error
                 } else {
                 //get main queue to comunicate back to user
                 DispatchQueue.main.async(execute: {
                 let message = parseJSON["message"] as! String
                 //appDelegate.errorView(message: message)
                 appDelegate.infoView(message: message, color: colorSmoothRed)
                 print("Erro sem sucesso\(parseJSON)")
                 catch {
                 DispatchQueue.main.async(execute: {
                 let message = "Erro de Comunicação\(error)"
                 appDelegate.infoView(message: message, color: colorSmoothRed)
                 // if unable to proceed request
                 } else {
                 // get main queue to comunicate back to user
                 DispatchQueue.main.async(execute: {
                 let message = error!.localizedDescription
                 appDelegate.infoView(message: message, color: colorSmoothRed)
                 print("sem comunicação!")

           // } else {
           //     print("Sem sucesso!")
        // launch prepared session
        } .resume()

The message is: "Erro ComunicaçãoError
Domain = NSCocoaErrorDomain code=3840" JSON ....

I bet that try JSONSerialization when the API returns data is throwing an error (JSON parse error, like what was printed). If an error is thrown, it gets handled in the catch block, not at the guard; if you change your try JSON... to a try? JSONSerialization.jsonObject(...) that will make it fail at the guard instead (giving you "Error parsing parsing" instead).

These two ways of expressing a try give equivalent results (except one lets you see the actual error):

func pattern1() {
    guard let result = try? throwingMethod() else {
        print("I will print here if there's an error. We don't have access to the actual error, so I can't print it")

    print("We have a value: \(result)")

func pattern2() {
    do {
        let result = try throwingMethod()
        print("We have a value: \(result)")
    } catch {
        print("I will print here if there's an error. Here's the error: \(error)")

The tradeoff in this pattern: "can I get the error's value" vs "can I use one fewer indentation level once I'm holding the result of the throwing method". A third pattern: mark pattern3 as throwing, and pass the error to be someone else's responsibility... You can immediately access the value without a level of indentation being created, and no guard or do block at all!