stripe webhook account.updated is not working - php

Question

I am trying to send an (simple test) email when I receive an account.updated call for a custom account from Stripe API. My other webhooks to create charges and inform customers about successful or failed charges work like this, but here I get an error 500 (I can see that in the dashboard of the custom account) and the mail is NOT send, so I am not sure what I am doing wrong here. My code looks like this:
<?php
require_once('vendor/autoload.php');
// Set your secret key: remember to change this to your live secret key in production
// See your keys here: https://dashboard.stripe.com/account/apikeys
\Stripe\Stripe::setApiKey("sk_test_XXXX");
// Retrieve the request's body and parse it as JSON
$input = #file_get_contents("php://input");
$event_json = json_decode($input);
// Verify the event by fetching it from Stripe
$event = \Stripe\Event::retrieve($event_json->id);
// Do something with $event
if ($event->type == 'account.updated') {
// The E-Mail message to send to inform about a succeeded charge
$message = 'test';
// Send the E-Mail
mail('test#example.com', 'We need more info about you!', $message);
}
http_response_code(200); // PHP 5.4 or greater
Thank you for your help!

Answer 1

If you look at your web server's error.log (usually accessible from your hosting control panel or in /var/log/) do you see more detail on what's causing the 500?
Could it be $event = \Stripe\Event::retrieve($event_json->id); failing?
If the event is occurring directly on a connected account, you may also need to pass the account id to retrieve it.
See here for a bit more context,
https://stripe.com/docs/connect/webhooks
The code would be more like:
$event = \Stripe\Event::retrieve(
array("id" => $event_json->id),
array("stripe_account" => $event_json->account));
https://stripe.com/docs/connect/authentication#authentication-via-the-stripe-account-header