Recaptcha v3

Index:

<?php
define("RECAPTCHA_V3_SITE_KEY", "XXX");
?>
<script src="https://www.google.com/recaptcha/api.js?render=<?php echo RECAPTCHA_V3_SITE_KEY; ?>"></script>
<script>
grecaptcha.ready(function() {
  grecaptcha.execute('<?php echo RECAPTCHA_V3_SITE_KEY; ?>', {action: 'contato'}).then(function(token) {
    document.getElementById('recaptchaResponse').value = token;
  });
});
</script>

<input type="hidden" name="recaptcha_response" id="recaptchaResponse">

Send:

$recaptcha_secret = 'ZZZ';
$recaptcha_response = $_POST['recaptcha_response'];

$recaptcha = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret=' . $recaptcha_secret . '&response=' . $recaptcha_response);
$recaptcha = json_decode($recaptcha, true);

if (isset($recaptcha['score']) && $recaptcha['score'] >= 0.5) {
  $erro = '';
}