I faced the issue I can’t solve right now. I have an error axios, the code is not so long, but I have no idea where exactly to look. So I just wondered maybe someone could help me out ? The problem is somewhere in the client code, because I tried to test it with POSTMAN then I get status OK 200, but when I try to log in from UI then I get axios error.

const url = BACKEND_URL;
     console.log(`${url}/api_app`);
     const logo = require("../../images/logo-pinigine.png");

     const credentials = `${validUsername}:${validPassword}`;
     const encodedCredentials = encode(credentials);
     const instance = axios.create({
      baseURL: `${url}/api_app`,
      headers: {
      Authorization: `Basic ${encodedCredentials}`,
      Accept: "application/json",
     },
    });

    const handleLogin = async () => {
    if (isInputValid()) {
      if (isHuman) {
         try {
          var returnValue = 0;
          const res = await instance.post(`/app_actions.php`, {
            action: "find_user_by_email",
            email: email,
            password: password,
          });
          const data = res.data;

          if (data.success == 1) {
            returnValue = data.success;

            setRajonu_arr(data.data);
          } else {
            returnValue = data.success;
            toaster.show({
              message: data.msg,
              type: "error",
              position: "middle",
              duration: 2000,
            });
          }
        } catch (error) {
          console.log(error);
        }
        if (returnValue !== 0) {

          changeRajonaiModalVisible(true);
    }
  } else {
    toaster.show({
      message: "Pirma pažymėkite, kad nesate robotas.",
      type: "error",
      position: "middle",
      duration: 2000,
    });
  }
 }
};

<?php

header('Access-Control-Allow-Origin: *');
header('Content-Type: application/json');
header('Access-Control-Allow-Methods: GET, POST, OPTIONS, DELETE, PUT');
header('Access-Control-Allow-Headers: Access-Control-Allow-Headers,Content-Type,Access-Control-Allow-Methods, Authorization, X-Requested-With');

require_once($_SERVER['DOCUMENT_ROOT'] . '/db.php');
require_once($_SERVER['DOCUMENT_ROOT'] . '/classes/System.php');
require_once($_SERVER['DOCUMENT_ROOT'] . '/classes/functions.php');
$json = file_get_contents('php://input');
$data = json_decode(file_get_contents("php://input"));
//require_once($_SERVER['DOCUMENT_ROOT'] . '/ajax/helpers.php');
error_reporting(E_ALL);
// Set the username and password for authentication
global $mysqli;
//is bendrines weekly nustatymas kad ateitu
$validUsername = nustatymai_par_reiksme($mysqli, 'validApiUsername');
$validPassword = nustatymai_par_reiksme($mysqli, 'validApiPassword');
//print_r(" validUsername  ".$validUsername."  validPassword   ".$validPassword);

//$validUsername = 'username';
//$validAPIUsername = 'password';
// Check if the Authorization header is set
if (!isset($_SERVER['PHP_AUTH_USER']) || !isset($_SERVER['PHP_AUTH_PW'])) {
    header('HTTP/1.1 401 Unauthorized');
    header('WWW-Authenticate: Basic realm="API Authentication"');
    exit;
}

// Verify the provided credentials
$username = $_SERVER['PHP_AUTH_USER'];
$password = $_SERVER['PHP_AUTH_PW'];

//$username = $_GET['PHP_AUTH_USER'];
//$password = $_GET['PHP_AUTH_PW'];
if ($username !== $validUsername || $password !== $validPassword && isset($data->system_id)) {
    header('HTTP/1.1 401 Unauthorized');
    exit;
}

// Authentication successful, handle API requests
if (isset($_POST['action'])) {
    $action = $_POST['action'];

    // Call the appropriate function based on the action
    switch ($action) {
        case 'find_user_by_email':
            // Call function1
            find_user_by_email();
            break;
        default:
            // Invalid action, return an error response
            $response = ['error' => 'Invalid action'];
            echo json_encode($response);
            break;
    }
} else {
    // No action specified, return an error response
    $response = ['error' => 'No action specified'];
    echo json_encode($response);
}

function find_user_by_email()
{
    global $mssql, $mysqli;
    $return = [];
    $email = $_POST['email'];

    $System = new System();

    if (isset($email)) {
        $systems_rajonai = $System->getSystemRajonaiList($email);
        if (count($systems_rajonai) > 0) {
            $return['msg'] = 'rajonai gauti';
            $return['data'] = $systems_rajonai;
            $return['success'] = 1;
        } else {
            $return['msg'] = 'Tokio vartotojo E-Maitinimas sistemoje nėra';
            $return['success'] = 0;
        }
    } else {
        $return['msg'] = 'neivestas email';
        $return['success'] = 0;
    }
    echo json_encode($return);
}
?>

And I have this PHP file
I don’t know about php, this file was built for me

I expect to have status ok 200 from client side

I checked the other topics but wasn’t helpful, because there was the main problem that he should enable CORS in server side which I am already enabled also I am using credentials which is encoded and none of them was used. And I am using PHP differently than others, maybe there can be the issue aswell. And also I am using Authorization: Basic Auth, maybe I missed something there in client side.