here's the thing want the invalid parameters error in response but the parse api returns this error

[zerodark30]

Fatal error: Cannot use object of type stdClass as array in C:\xampp\htdocs\ielts\parse.php on line 190

my code is
$loginUser = new parseUser;
$loginUser->username = $testUser['username'];
$loginUser->password = $testUser['password'];

    $returnLogin = $loginUser->login();
    $objArray = get_object_vars($returnLogin);
    echo "<pre>";print_r($objArray);
    $freking_object_id = $objArray['objectId'];
    echo $freking_object_id;