Facebook javascript api - webhook

Question

i am having a problem to do a webhook with the facebook api on a lead ads form. Last day it was working like a charm. On the 'Lead Ads Testing Tool' i received a status = success. Now i received a status = failure, error code = 102, error message = server failure

image of the error 102

Anyone know this issue ?

here my webhook.php :

if (isset($_GET['hub_verify_token'])) {
   if ($_GET['hub_verify_token'] === 'your verify token') {
    echo $_GET['hub_challenge'];
    return;
} else {
    echo 'Invalid Verify Token';
    return;
}
}

$input = json_decode(file_get_contents('php://input'), true);
$emailfrom = "test@test.com";
$emailto = "my@email.com";

$subject = "You've got a new submission Test";
$headers = "From: " . $emailfrom . "\r";
$headers .= "Reply-To: ". $emailfrom . "\r";
$headers .= "MIME-Version: 1.0\r";
$headers .= "Content-Type: text/html; charset=utf-8\r";
$body = 'hello';
mail($emailto, $subject, $body, $headers);

and the callback_url is good = "success": true image graph api subscription to webhook

Thanks