Using POST and WebRequest in Unity

Hey!
I have a mini-system with MySQL and PHP and I need to connect it with Unity, for login, save high scores, etc. I used the example from here: https://docs.unity3d.com/ScriptReference/Networking.UnityWebRequest.Post.html
But when I call the Login method from a Canvas button, the system returns a successful result (using Debug.Log function), but the PHP file doesn't detect POST from Unity. Now, I guess the problem is on the PHP file, but I didn't find any issue with POST logic, so I can't confirm this statement.
I'm using XAMPP to create a server with MySQL and PHP.

Here is my class for connection

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.SceneManagement;
 using UnityEngine.Networking;
 
 public class Server : MonoBehaviour
 {
     public InputField username;
     public InputField password;
 
     public void Login() {
         StartCoroutine(Upload());
     }
 
     IEnumerator Upload()
     {
         WWWForm form = new WWWForm();
         form.AddField("username", username.text);
         form.AddField("password", password.text);
         
         UnityWebRequest www = UnityWebRequest.Post("http://localhost/school-system/unity/index.php", form);
         
         yield return www.SendWebRequest();
         if (www.result != UnityWebRequest.Result.Success)
         {
             Debug.Log(www.error);
         }
         else
         {
             Debug.Log("Form upload complete!");
         }
     }
 }

And here is my index.php (I'm not using any hash function for passwords, because the system at moment is only for tests)

 <?php
     include '../connection.php';
 
     if(isset($_POST['username']) && isset($_POST['password'])) {
         $username = $_POST['username'];
         $password = $_POST['password'];
         $sql = "SELECT COUNT(*) FROM user 
         WHERE user_nickname = '$username' AND user_password = '$password'";
         $query = mysqli_query($connection, $sql);
         $row = mysqli_fetch_row($query);
         if($row[0] != 0) {
             $sql = "SELECT user_nickname, user_password FROM user 
             WHERE user_nickname = '$username' AND user_password = '$password'";
             $query = mysqli_query($connection, $sql);
             $row = mysqli_fetch_row($query);
             echo $row[0]." - ".$row[1];
         } else {
             echo "error";
         }
     }
 ?>