Receiving webhook data and save them in db

I want to handle data, that is sended by a trello webhook. There for the webhook posts to a url like site.com/tracker.php

In the tracker.php I want to save the data in a database. For that I need to get some params.

This is a example of the code I receive (https://trello.com/docs/gettingstarted/webhooks.html):

{
   "action": {
      "id":"51f9424bcd6e040f3c002412",
      "idMemberCreator":"4fc78a59a885233f4b349bd9",
      "data": {
         "board": {
            "name":"Trello Development",
            "id":"4d5ea62fd76aa1136000000c"
         },
         "card": {
            "idShort":1458,
            "name":"Webhooks",
            "id":"51a79e72dbb7e23c7c003778"
         },
         "voted":true
      },
      "type":"voteOnCard",
      "date":"2013-07-31T16:58:51.949Z",
      "memberCreator": {
         "id":"4fc78a59a885233f4b349bd9",
         "avatarHash":"2da34d23b5f1ac1a20e2a01157bfa9fe",
         "fullName":"Doug Patti",
         "initials":"DP",
         "username":"doug"
      }
   },
   "model": {
      "id":"4d5ea62fd76aa1136000000c",
      "name":"Trello Development",
      "desc":"Trello board used by the Trello team to track work on Trello.  How meta!\n\nThe development of the Trello API is being tracked at https://trello.com/api\n\nThe development of Trello Mobile applications is being tracked at https://trello.com/mobile",
      "closed":false,
      "idOrganization":"4e1452614e4b8698470000e0",
      "pinned":true,
      "url":"https://trello.com/b/nC8QJJoZ/trello-development",
      "prefs": {
         "permissionLevel":"public",
         "voting":"public",
         "comments":"public",
         "invitations":"members",
         "selfJoin":false,
         "cardCovers":true,
         "canBePublic":false,
         "canBeOrg":false,
         "canBePrivate":false,
         "canInvite":true
      },
      "labelNames": {
         "yellow":"Infrastructure",
         "red":"Bug",
         "purple":"Repro'd",
         "orange":"Feature",
         "green":"Mobile",
         "blue":"Verified"
      }
   }
}

And this is my current tracker.php file:

<?php

$json = $_POST["actions"];
$action = json_decode($json);
$action_id = $action->id;
$card_id = $action->data->card->id;
var_dump($array);

My questions:

• Is the $_POST["actions"] right? Or what do I need inside the []
• Is the way I want to get the $action->data->card->id right?
• Is there any way to see the result of the var_dump? Dont know how to see the result of an webhook post..

I had to use this:

$json = file_get_contents('php://input');
$action = json_decode($json, true);

As far as I understand the json request is not automaticly split into the $_POST. Thus you have to use the input itself.

The true-parameter in json_decode is needed to get an associative array. Without it I only got an empty array.