Bridge callback endpoints timeout

The Bridge API is working in general - the /info or /list endpoints respond like expected. But the Callback endpoints just run in a timeout.

GET http://192.168.1.137:8080/callback/add?url=http%3A%2F%2Fhttpdump.app%2Fmy-dump&token=mytoken

Takes a while and then just responds with:

org.apache.http.conn.HttpHostConnectException: Connect to 192.168.1.137:8080 [/192.168.1.137] failed: Operation timed out

What can I do to add a callback so that I can get updates from my Opener?