Webhook is never triggered

[Radon8472]

I tried to run a task, that should trigger a webhook when finished (Like example webhook_send).

That is my code:

require_once('vendor/autoload.php');

use Ilovepdf\OfficepdfTask;

// Load my keys into $keys
$myTask = new OfficepdfTask($keys[0],$keys[1]);
$file1 = $myTask->addFile('my-test.ppt');
$myTask->setOutputFilename('outfile-office.pdf');

$myTask->setWebhook('http://my-url.de:20000/pdf-download-hook');

// We don't download here because with the webhook we ordered the files must be processed in background.
// Notification will be sent once it's ready

//   $myTask->execute(); // see info add "Own research"

Expected behavior:

• WebHook-url should be triggered, when task is done.

Actual behavior:

• WebHook is never triggered

Own reseach:

• I noticed, that the method setWebhook() does not trigger any server-requests, so I tried to add

  $myTask->execute();
  

  because documentation says webhook should be send with POST https://{server}/v1/process. But the webhook still is not triggered.
• the same script works fine, when I remove "setWebhook" and add a $myTask->download() at the end -> so I`m quite there are no issues with api key, internet connection or anything similar.
• I sure my webhook url is reachable from public internet too

EDIT: When I add the same webhook as webhook into my global api config, it is called successfull, but dynamical adding webhooks via Task->setWebhook() seems to have no effect.