Github Webhook: Can't connect

Question

I want to use githubs webhooks for autodelpoyment. I set up a sinatra container with this image: https://hub.docker.com/r/tongueroo/sinatra/ and created a very simple sinatra server.

The remote server is accessable via postman from my local machine. But when i try to send the webhook an error occours: We couldn’t deliver this payload: failed to connect to host

Firewall seems to be fine and my remote server can pull my git repo

Any suggestions what the problem may cause?