Slack webhook notifications not working

[MrGreenTea]

I've been trying to get notified in a slack channel if Postiz posts a scheduled post. I've created a slack app and copied the webhook URL from there.

Using it with curl like described in the slack docs (curl -X POST -H 'Content-type: application/json' --data '{"text":"Hello, World!"}' $WEBHOOK_URL) works fine from my terminal. But I get no notifications by Postiz and clicking on "send test" does nothing.

What am I missing? What can I do?

The logs show no errors or anything. This is the last log output:

event to dispatch:  {
  pattern: 'webhooks',
  data: {
    id: 'digest_<XXX>,
    options: { delay: 60000 },
    payload: {
      org: '<ORG_ID>',
      since: '2025-05-05T14:30:00'
    }
  }
}
Email sender information not found in environment variables