Facebook sends empty POST to a webhook

Question

I am trying to install a webhook for leadgen event for my page via a facebook app. So I have:

1. Facebook Page where leads come from
2. Facebook App
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Answer 1

This code works for me...

if (!empty($_REQUEST['hub_mode']) && $_REQUEST['hub_mode'] == 'subscribe' && $_REQUEST['hub_verify_token'] == "") {
    echo $_REQUEST['hub_challenge'];
} else {
    $data = json_decode(file_get_contents("php://input"), true);
    file_put_contents('logFB.txt', print_r($data, true));
}  

First part is for verifying webhook, second for getting data from facebook webhook.

Hope this will help...