Error: JSON parse error: Invalid value.

First I apologize. I am using google translate to ask the question.

I am trying to make a logging system in a mysql database with unity. At the moment, the database is local. But when sending the data, or rather when receiving it, the following error occurs:

 ArgumentException: JSON parse error: Invalid value.
 UnityEngine.JsonUtility.FromJson (System.String json, System.Type type) (at <3e7f43c38e214491a21ee815b941dbb6>:0)
 UnityEngine.JsonUtility.FromJson[T] (System.String json) (at <3e7f43c38e214491a21ee815b941dbb6>:0)
 NetworkManager+<CO_CreateUser>d__1.MoveNext () (at Assets/Scripts/NetworkManager.cs:30)
 UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) (at <9899854e5b05425ab27d31f737cde095>:0)

Registration should occur when the user presses a button. The method that is executed when the button is pressed is in a script called MainMenuController. The method is the following:

 public void SubmitRegistration(){
 
         if (nameCountrySelected == ""){
             UserError(3);
             return;
         }
 
         if(!EmptyInputField()){
             UserError(1);
             return;
         }
 
         if (inpPasswordRegistrationMenu.text != inpConfirmPasswordRegistrationMenu.text){
             UserError(2);
             return;
         }
 
         CommunicationMenu.SetActive(true);
 
         networkManager.CreateUser(inpNameRegistrationMenu.text, inpEmailRegistrationMenu.text, 
         inpPasswordRegistrationMenu.text, inpNickNameRegistrationMenu.text, nameCountrySelected, 
         delegate (Response response){
             txtComm.text = response.message;
         }
         );
     }

Where txt Comm.text is a TEXTFIELD that should display the message it receives. The script that the "Assets/Scripts/NetworkManager.cs:30" error refers to is as follows:

 public class NetworkManager : MonoBehaviour{
 
     public void CreateUser(string UserName, string email, string pass, string nickName, string country, Action <Response> response){
         
         StartCoroutine(CO_CreateUser(UserName, email, pass, nickName, country, response));
     }
 
     private IEnumerator CO_CreateUser(string UserName, string email, string pass, string nickName, string country, Action<Response> response){
 
         WWWForm form = new WWWForm();
         form.AddField("UserName", UserName);
         form.AddField("email", email);
         form.AddField("pass", pass);
         form.AddField("nickName", nickName);
         form.AddField("contry", country);
         
         UnityWebRequest www = UnityWebRequest.Post(GameConstants.URL_ADDRESS_CREATE_USER, form);
         yield return www.SendWebRequest();
 
         response(JsonUtility.FromJson<Response>(www.downloadHandler.text));
 
         if (www.result != UnityWebRequest.Result.Success) //www.result
         {   
             Debug.Log(www.error);
         }
         else 
         {
             Debug.Log("Form upload complete!");
         }
     }
 }
 
     [Serializable] public class Response{
     public bool done;
     public string message;
 }

It is on line 30 where the error occurs.

 response(JsonUtility.FromJson<Response>(www.downloadHandler.text));

The php code that is executed:

 <?php
 include "dbConnection.php";
 include "ConstantsFile.php";
 include "functions.php";
 
 $UserName = $_POST['UserName'];
 $email = $_POST['email'];
 $pass = hash("sha256", $_POST['pass']);
 $nickName = $_POST['nickName'];
 $contry = $_POST['contry'];
 
 
 $sql = "SELECT Name_User FROM users WHERE Name_User = '$UserName'"
 $result = $pdo->query($sql);
 
 if($result->rowCount() > 0){
   MessageAfterQuery(false, ERROR_NAME_USER);
   exit();
 }
 else{
   $sql = "SELECT Email_User FROM users WHERE Email_User = '$email'"
   $result = $pdo->query($sql);
 
   if($result->rowCount() > 0){
     MessageAfterQuery(false, ERROR_EMAIL);
     exit();
   }
 }
 else{
   $sql = "INSERT INTO users(Name_User, Email_User, Password_User,
   Nick_User, Country_User)
   VALUES ('[$UserName]','[$email]','[$pass]','[$nickName]','[$contry]')";
   $pdo->query($sql);
 
   MessageAfterQuery(true, CONFIRM_CREATE_USER);
   exit();
 }
 ?>

The function that must send the information in Json "MessageAfterQuery" is this:

 <?php
 include "ConstantsFile.php";
 
 $data ="";
 
 function MessageAfterQuery($boolConfirm, $messageQuery){
   $data = array('done'=> $boolConfirm, 'message'=> $messageQuery);
   Header('Content-Type: application/json');
   echo json_encode($data);
   exit();
 }
 ?>

I have searched the internet and I have tried different alternatives but I cannot solve this error.

I don't know what part of the code is wrong.